"     V 


_     "•» 


ELEMENTARY 
CHEMISTRY 


By 

C.   E.    LINEBARGER 

Instructor  in  Chemistry  in  the 
Lake  View  High  School,  Chicago, 
and  Editor  of  "  School  Science" 


RAND,  McNALLY  &  COMPANY 

CHICAGO  NEW  YORK  LONDON 


GENERAL1 

i  C 


Copyright,  1904 
By  C.  E.  LlNEBARGER 


Chicago 


THE  PREFACE 

A  COURSE  in  elementary  chemistry  suitable  for 
the  average  high-school  student  should  give  a 
description  of  the  common  elements,  their  compounds, 
and  their  reactions,  sufficiently  clear  and  full  to  enable 
him  to  form  correct  conceptions  of  the  nature  of  the 
changes  that  are  going  on  around  him.  But  it  should 
do  more  ;  as  far  as  is  possible  in  an  elementary  course, 
it  should  provide  him  with  a  thorough  groundwork  in 
the  simpler  laws  and  theories  of  modern  chemistry. 
This  gives  meaning  and  coherence  to  what  would  other- 
wise be  fragments  of  knowledge,  and  lays  a  solid  foun- 
dation for  the  continuation  of  the  study  of  chemistry. 

The  descriptive  matter  should  impose  as  little  strain 
as  possible  on  the  student's  memory.  To  accomplish 
this  the  facts  should  be  properly  coordinated  with  one 
another  and  duly  correlated  with  the  experiences  of 
everyday  life.  General  points  of  view  should  be  em- 
phasized and  isolated  details  suppressed.  Important 
historical  items  should  be  mentioned,  for  they  put  life 
into  the  subject  and  give  it  perspective. 

The  laws  of  chemistry  should  be  introduced  in  im- 
mediate connection  with  the  discussion  of  those  sub- 
stances which  first  present  typical  applications  of  each 
law.  The  treatment  of  the  laws  should  be  full  and 
varied.  Reference  to  them  should  be  made  frequently 
throughout  the  course,  so  that  they  may  become  a  per- 
manent working  possession  of  the  student. 

The  modern  theories  of  physical  chemistry  should 
receive  the  attention  their  importance  demands.  They 
are  indeed  no  longer  modern,  for  they  have  stood  the 

[in] 


iv  Elementary  Chemistry 

test  of  time.  While  anything  like  a  thoroughgoing 
treatment  is,  of  course,  impracticable  in  an  elementary 
text,  yet  the  explanations  which  these  theories  suggest 
in  regard  to  phenomena  may  in  several  instances  be 
given  with  profit. 

Industrial  chemistry  demands  recognition,  and 
although  it  may  not  be  feasible  to  enter  into  a  full  dis- 
cussion of  many  industrial  processes,  yet  the  details  of 
a  few  should  certainly  be  given,  so  that  the  outlines  of 
others  may  be  the  more  readily  understood.  The  best 
way  to  get  adequate  notions  of  industrial  operations 
is  by  excursions  to  works.  But  the  description  of  a 
process,  accompanied  by  diagrams  designed  to  bring 
out  the  important  features  and  the  general  run  of  the 
process,  assists  in  preparing  students  for  excursions. 
They  are  thereby  saved  from  being  overwhelmed  by 
the  mass  of  detail  presented  on  inspection  of  a  plant ; 
they  recognize  its  salient  features  more  readily  ;  they 
know  for  what  to  look  and  how  to  look  ;  they  correctly 
grasp  the  connection  between  the  industrial  operations 
and  the  underlying  chemical  principles. 

The  energy  aspect  of  chemistry  should  not  be 
entirely  neglected.  Elementary  notions  of  thermo- 
chemistry illustrated  by  simple  reactions  should  be 
dwelt  upon  here  and  there  in  the  course. 

Theories  should  not  be  considered  until  after  the 
student  has  acquired  some  knowledge  of  the  facts  and 
laws  of  chemistry.  Their  presentation  should  be  such 
as  not  to  fail  to  give  correct  notions  of  their  real  value 
and  their  relation  to  facts  and  laws. 

The  purpose  of  exercises  and  problems  is  not  merely 
to  test  the  memory,  but  rather  to  develop  power  of 
constructive  thought  and  creative  imagination.  The 
exercises  should  be  so  selected  and  worded  that  their 
answers  are  not  found  explicitly  stated  in  the  preceding 


The  Preface  v 

chapter.  A  comparison  of  facts  and  an  exercise  of 
judgment  should  be  required  in  framing  the  answers. 
Most  of  the  problems  should  be  taken  directly  from  the 
works  of  the  pioneers  in  chemical  investigation,  and 
should  be  chosen  more  for  their  chemical  than  for  their 
mathematical  value. 

Laboratory  and  text-book  work  should  go  hand  in 
hand.  In  certain  parts  of  the  subject  the  laboratory 
has  to  be  subordinated  to  the  class  room,  and  in  others, 
the  class  room  to  the  laboratory.  But,  all  in  all,  the 
closest  correlation  possible  should  be  maintained  be- 
tween the  two.  The  experiments  should  be  simple  but 
not  trivial.  Each  one  should  lay  special  emphasis  upon 
but  a  single  point.  A  reasonable  amount  of  simple 
quantitative  work  involving  the  careful  manipulation 
of  simple  apparatus  will  help  to  develop  the  power  of 
observation  and  to  prevent  slovenliness  in  the  labo- 
ratory. 

No  amount  of  written  description  and  sectional 
drawings  can  make  the  secondary-school  pupil  see  how 
his  apparatus  should  be  put  together  .so  well  as  a  photo- 
graph. Hence  an  elementary  text-book  should  be  illus- 
trated in  the  most  graphic  manner.  The  author  believes 
that  a  photograph  of  the  apparatus  the  pupil  is  to  handle 
furnishes  a  better  illustration  than  the  sectional  draw- 
ings commonly  used  in  science  text-books.  Most  of  the 
illustrations  in  this  book  have  been  secured  by  setting 
up  the  actual  apparatus,  photographing  it,  and  then 
silhouetting  it  in  the  half-tone  plates.  Where  internal 
construction  needs  to  be  shown  the  sectional  drawing 
has  been  used  as  before. 

Believing  that  these  are  the  requisites  of  a  practical 
elementary  text-book  in  chemistry,  the  author  has 
attempted  to  meet  them  in  the  preparation  of  this 
work.  He  has  aimed  to  economize  teaching  energy 


vi  Elementary  Chemistry 

and  to  provide  for  flexibility  of  the  course.  With  that 
end  in  view  he  has  made  the  typographical  arrange- 
ment such  that  certain  topics  may  be  readily  omitted 
without  interfering  with  the  continuity  of  the  course. 
Not  that  he  feels  that  such  topics  should  be  omitted,  but 
because  he  recognizes  the  need  which  frequently  arises 
for  shortening  the  course,  and  wishes  to  indicate  what 
may  be  omitted  with  least  loss. 

The  author  takes  pleasure  in  thanking  the  following 
teachers  for  valuable  criticisms  on  the  manuscript:  Mr. 
Harry  D.  Abells,  Morgan  Park  Academy,  Morgan  Park, 
III.;  Dr.  C.  E.  Boynton,  Robert  Waller  High  School, 
Chicago ;  Miss  Louella  Chapin,  South  Division  High 
School,  Chicago;  Mr.  Harry  Clifford  Doane,  Central 
High  School,  Grand  Rapids,  Mich.;  Mr.  Oscar  R.  Flynn, 
Hyde  Park  High  School,  Chicago;  Mr.  Albert  C.  Hale, 
Boys'  Higli  School,  Brooklyn,  N.  Y.;  Prof.  Alexander 
Smith,  The  University  of  Chicago;  Mr.  Charles  M. 
Turton,  South  Chicago  High  School,  Chicago;  Prof. 
Theodore  Whittelsey,  Northwestern  University ;  Mr. 
C.  M.  Wirick,  R.  T.  Crane  Manual  Training  High 
School,  Chicago;  Mr.  E.  C.  Woodruff,  Lake  View 
High  School,  Chicago ;  and  Mr.  F.  J.  Watson,  William 
McKinley  High  School,  Chicago. 

He  also  wishes  to  acknowledge  his  indebtedness  to 
the  following  teachers  who  have  read  the  proofs  of  the 
book  and  offered  many  helpful  suggestions  :  Prof. 
Alexander  Smith,  The  University  of  Chicago;  Prof. 
G.  C.  Caldwell,  Cornell  University,  Ithaca,  N.  Y.;  Mr. 
Charles  M.  Turton,  South  Chicago  High  School,  Chicago; 
Mr.  E.  C.  Woodruff,  Lake  View  High  School,  Chicago. 

His  thanks  are  also  due  Mr.  W.  S.  Davis  and  Mr.  E. 
C.  Woodruff  for  the  preparation  of  the  illustrations. 

C.    E.    LlNEBARGER. 

Chicago,  April,  1904. 


THE  TABLE  OF  CONTENTS 


PAGE 

The  Preface  .     .  v 


CHAPTER  I 

Introductory 

Nature  —  Science  —  Matter  and  Energy  —  What  We 
Study  in  Chemistry  —  Physical  and  Chemical  Changes  — 
Physical  and  Chemical  Properties — Identification  of  Sub- 
stances—  Tests  —  Chemical  Action  —  Cause  of  Chemical 
Change  —  Elements  and  Compounds  —  Metals  and  Non- 
Metals —  Mixtures  and  Compounds  —  Conservation  of  Mat- 
ter and  Energy  —  Immutability  of  the  Elements — Exer- 


CHAPTER    II 

The  General  Properties  of  Gases 14 

States  or  Conditions  of  Matter  —  Necessity  for  a 
Preliminary  Study  of  Gases  —  Volume,  Pressure,  and 
Temperature  —  Charles'  Law  —  Absolute  Temperatures  — 
Boyle's  Law  —  Density  and  Specific  Gravity  —  Standard 
Conditions  —  Reduction  of  the  Volume  of  a  Gas  to  Stan- 
dard Pressure  —  Reduction  of  the  Volume  of  a  Gas  to 
Standard  Temperature  —  Correction  for  Vapor  Tension  — 
Problems. 

CHAPTER  III 

Oxygen  and  Ozone 26 

Oxygen — Occurrence  —  Preparation —  Properties — No- 
menclature —  Oxidation  and  Reduction  —  Uses  —  Ozone  — 
Allotropy  —  Occurrence  —  Preparation  —  Properties. 

CHAPTER  IV 

Hydrogen 33 

Occurrence  —  Preparation — Properties  —  Nascent  State 
— Uses  —  Exercises  —  Problems, 
[vii] 


viii  Elementary  Chemistry 

\  CHAPTER   V 

The  Compounds  of  Oxygen  and  Hydrogen 38 

Water  —  Occurrence  —  Distillation  —  Filtration  —  For- 
mation —  Preparation  — Volumetric  Composition  by  Eudio- 
metric  Measurements  —  Volumetric  Laws  of  Chemical 
Combination  —  Law  of  Definite  Proportions  by  Mass  or 
Weight  —  Composition  of  Water  by  Gravimetric  Measure- 
ment—Relations Between  the  Laws  of  Definite  Propor- 
tions—Law of  Conservation  of  Matter  —  Synthesis  and 
Analysis  —  Analysis  of  Water  —  Chemical  Equations  — 
Physical  Properties  —  Solution  —  Supersaturation  — Water 
of  Crystallization  —  Efflorescence  and  Deliquescence  — 
Hydrogen  Dioxid  —  Preparation  —  Properties  —  Uses  — 
Law  of  Multiple  Proportions  —  Thermo-Chemistry  —  Ex- 
ercises—  Problems. 

CHAPTER   VI 

Nitrogen  and  Its  Hydrogen  Compounds 62 

Occurrence— Preparation — Properties —  A  rgon — Prep- 
aration —  Properties — Ammonia  —  Occurrence  —  Prepara- 
tion —  Properties  —  Uses  —  Hydrazin  and  Hydr azoic 
Acid —  Exercises  —  Problems. 

CHAPTER   VII 
Carbon •. 70 

Occurrence  —  General  Properties  —  Diamonds  —  Graph- 
ite —  Coal  —  Occurrence  —  Formation  —  Charcoal  —  Bone- 
black  —  Properties  and  Uses  of  Charcoal  and  Boneblack  — 
Lampblack  —  Coke  —  Gas  Carbon  —  Exercises. 

CHAPTER   VIII 
The  Compounds  of  Carbon  with  Oxygen      .     .     '.  "  .-;  .     ;     .     77 

Carbon  Dioxid —  Occurrence  —  Formation  and  Prep- 
aration —  Properties  —  Uses  —  Carbon  Monoxid —  Prep- 
aration —  Properties  —  Uses—  Exercises  —  Problems. 

CHAPTER  IX 
Some  Nitrogen  and  Hydrogen  Compounds  of  Carbon  ...     85 

Cyanogen  —  Occurrence  —  Preparation  —  Properties  — 
Hydrocyanic  A  cid—  Occurrence  and  Preparation  —  Prop- 
erties— Compounds  of  Carbon  and  Hydrogen  — 


The  Table  of  Contents  ix 

PAGE 

and  Inorganic  Chemistry  —  Hydrocarbons — Methane  or 
Marsh  Gas  —  Occurrence  —  Preparation  —  Properties  — 
Ethylene  or  Olefiant  Gas  —  Preparation  —  Properties  — 
Acetylene  —  Preparation — Properties  — Illuminating  Gas 

—  Old  Process — "Water  Gas" — Natural  Gas  —  Exercises 

—  Problems. 

CHAPTER  X 

The  Atmosphere 97 

Density  and  Use  —  Liquid  Air —  Composition  —  Air  Not 
a  Compound  — Solid  Matter  in  the  Air  —  Air  and  Life  — 
Exercises  —  Problems. 

>/    CHAPTER  XI 

Fire  and  Flame 104 

Source  of  Heat  and  Power  —  Combustion — Kindling 
Temperature  —  Flame  —  Combustible  and  Supporter  of 
Combustion  —  Spontaneous  Combustion  —  Luminosity  of 
Flame— Structure  of  Flame— Combustion  in  Candle  Flame 

—  Smoke  —  Temperature  of  Flames  —  Speed  of  Propaga- 
tion of  Flame  —  Combustion  in  a  Bunsen  Flame — Explo- 
sions —  Oxidizing  and  Reducing   Flames  ;     Blowpipe  — 
Exercises. 

^  CHAPTER  XII 

Combining  and  Elemental  Weights 1.18 

Symbols,  Formulas,  and  Equations — Combining 
Weights  —  Elemental  Weights  —  Symbols  —  Formulas  — 
Radicals — Formulas;  Combining  and  Elemental  Weights — 
What  a  Formula  Means— Determination  of  the  Formulas 
of  Compounds — Formula  Weights  —  Chemical  Equations 
— Balancing  Equations  —  General  Procedure  —  Volumes — 
Combustion  of  Organic  Compounds  Containing  Nitrogen 
— Usefulness  of  Chemical  Equations  —  Problems. 


. 


CHAPTER  XIII 


The  Atomic  Theory  — Valence 138 

Constitution  of  Matter  —  Atoms  and  Molecules;  Elec- 
trons—  The  Atomic  Theory —  Laws  Accounted  for  by  this 
Theory —  Valency —  Equations  in  Terms  of  Molecules  and 
Atoms— Value  of  Chemical  Equations — Variable  Valency 
—  Problems. 


x  Elementary  Chemistry 

\  CHAPTER  XIV 

PAGE 

Salts,  Acids,  and  Bases 146 

Early  Meaning  of  Salt,  Acid,  Alkali,  and  Base  —  Acid, 
Base,  Alkali,  and  Salt  Defined  —  Theory  of  Electrolytic 
Dissociation  —  lonization  Theory — Acid,  Alkalin,  and 
Neutral  Reactions  —  Indicators — Nomenclature  of  Acids, 
Bases,  and  Salts  —  Ions. 

CHAPTER  XV 

Nitrogen  Oxids  and  Oxacids 155 

Nature  of  Combination.     Nitrous  Oxid — Preparation 

—  Properties —  Uses  —  Other  Oxids  of  Nitrogen  —  Nitro- 
gen Trioxid  —  Nitrogen  Pentoxid — Nitrogen  Dioxid  and 
Tetroxid  —  Nitric    Acid  —  Occurrence  —  Preparation  — 
Properties — Fuming  Nitric  Acid  —  Uses — Nitrous  Acid 

—  Exercises  —  Problems. 

CHAPTER  XVI 

Preparation  and  Properties  of  Acids,  Salts,  and  Bases     .     .  164 

Preparation  of  Salts — By  Direct  Union  of  Elements 

—  By  Action  of  an  Acid  on  a  Metal  —  By  Action  of  an 
Acid  on  a  Base  —  By  Action  of  an  Acid  on  Salts  —  Prep- 
aration of  Acids  —  General    Method  —  Preparation   of 
Bases  —  Soluble  Bases — Insoluble  Bases. 

CHAPTER  XVII 

The  Halogens ;  Their  Hydrogen  and  Oxygen  Compounds       168 

Chlorin  —  Occurrence  —  Preparation  —  Manufacture  — 

Properties  —  Uses  —  Fluorin  —  Bromin  —  Occurrence  — 

Preparation  —  Properties —  Uses  —  lodin  —  Occurrence  — 

Preparation  —  Properties  —  Uses. 

Compounds  of  the  Halogens  with  Hydrogen  ;  the  Hydracids 

Hydrochloric  Acid — Occurrence —  Preparation — Prop- 
erties —  Uses  —  Hydrofluoric    A  cid  —  Preparation    and 
Properties  —  Hydrobromic  A  cid—  Preparation  and  Prop- 
erties—  Hydriodic  Acid  —  Preparation  and  Properties. 
Oxygen  Compounds  of  the  Halogens 

Exercises  —  Problems. 


The  Table  of  Contents  xi 

CHAPTER  XVIII 

The  Alkali  Metals 183 

In  General  —  Lithium  —  Sodium  and  Potassium  —  Oc- 
currence —  Preparation  —  Properties  —  Ammonium  —  Ox- 
ids  and  Hydroxids  of  the  Alkali  Metals  — Hydroxids  — 
Preparation  —  Ammonium  Hydroxid. 
Some  Important  Compounds  of  the  Alkali  Metals   .     .     .     .  188 

Halids  —  Sodium  Chlorid —  Salt  Making  —  Properties 
and  Uses  —  Ammonium  Chlorid — Potassium  Bromid  and 
lodid  —  Ammonium  Sulfid  —  Sodium  Sulfate  —  Prep- 
aration —  Properties  and  Uses  —  Potassium  Sulfate  —  So- 
dium  Carbonate  —  Le  Blanc's  Process  —  Solvay's  Am- 
monia-Soda Process  —  Properties  and  Uses — Sodium  Bi- 
carbonate —  Potassium  Carbonate  —  Potassium  Nitrate  — 
Potassium  Chlorate  —  Potassium  Cyanid  —  Exercises  — 
Problems. 

CHAPTER  XIX 

Equivalents  ;   Molecular  and  Atomic  Weights 200 

Equivalent  Weights  —  System  of  Equivalents  —  Electro- 
Chemical  Equivalents  —  Equivalent  Weights  of  Com- 
pounds —  Law  of  Equivalent  Proportions  —  Avogadro's 
Hypothesis  —  Determination  of  Molecular  Weights  by 
Means  of  Avogadro's  Hypothesis  —  Determination  of  Ato- 
mic Weights  by  Means  of  Avogadro's  Hypothesis  —  How 
to  Find  the  Atomic  Weight  of  Nitrogen  —  Equivalent  and 
Atomic  Weights  Compared  —  Equivalents  and  Valence  — 
Equivalence  and  Valence  of  Radicals  —  Basicity  and  Acid- 
ity—  Acid  and  Basic  Salts  —  Problems. 

CHAPTER  XX 

Methods  of  Determining  Molecular  and  Atomic  Weights     .  214 

Vapor  Density —  Other  Methods  of  Determining  Molec- 
ular Weights —  Analogy  Between  Gaseous  and  Dissolved 
States  —  Osmotic  Pressure  —  Depression  of  the  Freezing 
Point  of  Solutions — Elevation  of  Boiling  Points  —  Specific 
Heat — Dulong  and  Petit's  Law—  Determination  of  Ato- 
mic Weights  with  the  Aid  of  Dulong  and  Petit's  Law  — 
Problems. 


xii  Elementary  Chemistry 

CHAPTER  XXI 

PAGE 

Sulfur  and  Its  Compounds ".  223 

Occurrence  —  Preparation  —  Properties  —  Allotropic 
Forms  —  Uses  —  Hydrogen  Sulfid  —  Occurrence  —  Prep- 
aration —  Properties  —  Sulfids  —  Carbon  Bisulfid  —  Sulfur 
Dioxid—  Occurrence  —  Preparation  —  Properties— Uses  — 
Sulfur  Trioxid  —  Compounds  of  Sulfur,  Oxygen,  and  Hy- 
drogen —  Sulfuric  Acid—  Occurrence  —  Preparation  — 
Practice  of  the  Process  — Properties  — Uses— Fuming  or 
Pyrosulf uric  Acid  —  Exercises  —  Problems. 

CHAPTER  XXII 

Phosphorus,  Arsenic,  Antimony,  and  Bismuth 236 

Phosphorus  —  Occurrence  —  Preparation  —  Properties 

—  Red  Phosphorus —  Uses— Arsenic — Occurrence — Prep- 
aration —  Properties  —  Uses  —  Antimony  —  Occurrence  — 
Preparation  —  Properties  —  Uses  —  Bismuth —  Occurrence 

—  Preparation  —  Properties  —  Uses  —  Oxygen  Compounds 
— The  Oxids —  Phosphorus  Trioxid —  Phosphorus  Pentoxid 
— Arsenious  Oxid  or  Arsenic  Trioxid  —  Hydrogen  Com- 
pounds —  Phosphin  —  Halogen  Compounds  —  Phosphorus 
Chlorids  —  Acids  and  Salts — Hypophosphorous  Acid  — 
Phosphorous    Acid  —  Orthophosphoric    Acid  —  Pyrophos- 
phoric    Acid  —  Metaphosphoric     Acid — Phosphates     and 
Their  Uses  —  Exercises  —  Problems. 

CHAPTER  XXIII 

The  Alkalin  Earth  Metals  and  Their  Compounds     .     .     .     .251 

Occurrence  —  Preparation  —  Properties —  Uses  —  Oxids 
and  Hydroxids  —  Calcium  Oxid  —  Calcium  Hydroxid  — 
Some  Important  Salts  of  the  Alkalin  Earth  Metals  — 
Magnesium  Chlorid— Magnesium  Sulf  ate— Calcium  Chlorid 
— Calcium  Fluorid —  Bleaching  Powder  or  Chlorid  of  Lime 

—  Calcium    Carbonate  —  Limestone  —  Calcium    Sulf  ate  — 
Plaster  of  Paris— "Hard  Water "— Calcium  Phosphate  — 
Nitrates  of  the  Alkalin  Earth  Metals  —  Barium  Sulfate  — 
Exercises  —  Problems. 


T/ic  Table  of  Contents  xiii 

CHAPTER  XXIV 

Boron  and  Silicon 261 

Boron  —  Occurrence  —  Preparation  —  Properties  —  Bo- 
ric Acid  —  Borax  —  Silicon  —  Occurrence  —  Preparation  — 
Properties —  Silicon  Dioxid  —  Quartz  —  Amorphous  Silica 

—  Silicon  Hydrid  —  Silicon  Tetrachlorid  —  Silicon  Tetra- 
fluorid  —  Carborundum  —  Silicic  Acids  —  Glass  —  Proper- 
ties —  Mortar  —  Hydraulic   Cements  —  Exercises  —  Prob- 
lems. 

CHAPTER  XXV 

Zinc,  Cadmium,  and  Mercury ...  271 

Zinc  —  Occurrence  —  Metallurgy  —  Properties  —  Uses 
— Some  Important  Compounds  of  Zinc —  Zinc  Oxid  —  Zinc 
Chlorid — Zinc  Sulfate  —  Cadmium  —  Occurrence  and  Prop- 
erties —  Mercury  —  Occurrence  —  Preparation  —  Proper- 
ties—Uses—  Some  Important  Compounds  of  Mercury  — 
Salts  —  Mercuric  Oxid  —  Mercuric  Chlorid  —  Mercurous  . 
Chlorid  —  Mercuric  Sulfid  —  Mercury  Nitrates  —  Exercises 

—  Problems. 

CHAPTER  XXVI 

Aluminum 278 

Occurrence  —  Metallurgy  —  Properties  —  Uses  and  Al- 
loys —  Some  Important  Compounds  of  A  luminum  —  Salts 

—  Alums  —  Aluminum  Hydroxid  —  Aluminum  Oxid — Alu- 
minum Chlorid  —  Aluminum  Silicates — Porcelain — Stone- 
ware, Earthenware,  and  Bricks  —  Exercises  and  Problems. 

CHAPTER  XXVII 

Tin  and  Lead .286 

Tin  —  Occurrence  —  Metallurgy  —  Properties  —  Uses 
and  Alloy $>  — Principal  Compounds  of  Tin  —  Oxids  of  Tin 

—  Chlorids  of  Tin  — Tin  Sulfids  —  Lead—  Occurrence  — 
Metallurgy  —  Properties — Uses  and  Alloys  —  Some  Impor- 
tant Compounds  of  Lead —  Oxids  of  Lead  —  Chlorids  of 
Lead— Lead  Sulfate— Lead  Nitrate— Lead  Sulfid— Lead 
Carbonates  —  Lead  Acetate  —  Exercises  —  Problems. 


xiv  Elementary  Chemistry 

CHAPTER  XXVIII 

PAGE 

Copper,  Silver,  Gold,  and  Platinum 294 

Copper— Occurrence  —  Metallurgy  —  Properties  —  Uses 
and  Alloys  —  Some  Important  Compounds  of  Copper  — 
Copper  Oxids— Copper  Sulf ate  —  Copper  Nitrate  — Cop- 
per Sulfid  —  Stiver  —  Occurrence  —  Metallurgy  —  Prop- 
erties—  Uses  and  Alloys — Some  Important  Compounds 
of  Silver  —  Properties  —  Silver  Nitrate  —  Silver  Chlorid 

—  Silver  Bromid  and  lodid — Photography — 6W^— Oc- 
currence —  Metallurgy  —  Properties  —  Uses  and  Alloys  — 
Compounds  of  Gold  —  Platinum  —  Properties  —  Exercises 

—  Problems. 

CHAPTER  XXIX 

Iron,  Nickel,  and  Cobalt 306 

Iron  —  Occurrence  —  Metallurgy  —  Chemistry  of  the 
Process  —  Varieties  of  Iron  —  Cast  Iron  —  Wrought  Iron  — 
Steel  —  Manufacture  of  Steel  —  Bessemer  Process  —  Open- 
Hearth  Process  —  Properties  of  Iron  —  Compottnds  of  Iron 

—  Some  Important  Ferrous  and  Ferric  Compounds  —  Oxids 
and  Hydroxids  —  Iron  Sulfids — Iron  Chlorids  —  Iron  Sul- 
fates  —  Potassium  Ferro-  and  Ferri-Cyanids  —  'Nickel  — 
Occurrence,  and  Preparation  —  Properties  —  Uses — Nickel 
Compounds —  Cobalt — Exercises  —  Problems. 

CHAPTER  XXX 

Chromium  and  Manganese 321 

Chromium  —  Occurrence  and  Preparation  —  Properties 

—  Chromic  Compounds  —  Chromates  —  Manganese  —  Oc- 
currence and  Preparation  —  Properties  —  Manganese  Com- 
pounds —  Oxids  —  Manganous    Salts  —  Manganates  and 

.    Permanganates  —  Problems. 

CHAPTER  XXXI 

The  Periodic  System 326 

Development  of  the  System  —  Large  and  Small  Periods 
—  The  Value  of  the  Periodic  Law — Classification  of  the 
Elements  —  Prediction  of  Unknown  Elements  —  Problems. 


The  Table  of  Contents  xv 

CHAPTER  XXXII 

PAGE 

Some  Common  Organic  Compounds 332 

Composition  of  Carbon  Compounds  —  Valency  of  Car- 
bon; Graphic  Formulas  —  Nature  of  Carbon  —  Radicals  — 
.  Isomerism  and  Polymerism  —  Classification  of  Carbon 
Compounds  —  Hydrocarbons  —  A  Icohols  —  Methyl  Alco- 
hol—  Ethyl  Alcohol — Alcoholic  Liquors — Glycerin  — 
Aldehydes  —  Formaldehyde  —  Acetaldehyde  —  Ethers  — 
Ethyl  Ether  —  Acids  —  Acetic  Acid  —  Acetates  —  Vinegar 

—  Oxalic  Acid  —  Lactic  Acid  —  Tartaric  Acid  —  Esters  — 
Formation  —  Properties  —  Fats  and  Oils  —  Soaps —  Carbo- 
hydrates —  Sugars  —  Cane  Sugar  —  Glucose  —  Starch  — 
Dextrin  —  Cellulose  —  Benzene    Derivatives  —  Coal  Tar 

—  Benzene  —  Toluene  —  Phenol  —  Nitrobenzene  —  Anilin 

—  Benzoic    Acid  —  Benzoic    Aldehyde  —  Salicylic  Acid  — 
Naphthalene  —  Glucosides  —  Alkaloids. 

APPENDIX  A 
Qualitative  Analysis 

APPENDIX  B 
The  Metric  System  of  Weights  and  Measures     .     .     .        xvii 

APPENDIX  C 
Instruments  for  Weighing  and  Measuring xix 

APPENDIX  D 
Tables xxvi 

APPENDIX  E 

Significant  Figures  and  Forms  of  Record  in  Quantitative 

Work xxxi 

APPENDIX  F 
Laboratory  Equipment xxxvi 

APPENDIX  G 

Reference  Books xl 

The  Index  xliii 


ELEMENTARY  CHEMISTRY 


CHAPTER  I 


INTRODUCTORY 


1.  Nature.      Nature  is  the  name  given  to  the 
multitude  of  objects  all  about  us.     These  have  dif- 
ferent  properties   and    are   perpetually   changing. 
Man  has  a  firm  belief  founded  in  experience  that 
there  is  a  constancy  in  the  way  things  happen  — 
that  the  same  causes  acting  under  the  same  condi- 
tions always  produce  the  same  effects.     This  con- 
stancy gives  rise  to  the  Laws  of  Nature,  according 
to  which  the  phenomena,  i.  e.,  the  happenings  of 
nature,  occur.     A  Law  of  Nature  is  a  concise  state- 
ment covering  a  large  range  of  phenomena  ;  it  is  a 
general  fact  embracing  a  multitude  of  individual 
facts.     Man  often  tries  to  explain  phenomena  by 
means  of  hypotheses  upon  which  theories  may  be 
built.    A  collection  of  certain  of  the  Laws  of  Nature, 
together  with  the  facts  and  theories  pertaining  to 
theni,  constitutes  a  Branch  of  Science. 

2.  Science.     Science  is  classified  knowledge,  or 
"  the  knowledge  of  many,  methodically  arranged 
and  digested  so  as  to  be  attainable  by  one."     Men 
are  continually  investigating  nature  and  communi- 
cating their  discoveries  to  others.     The  facts  found 
are  compared,  sifted,  and  arranged.   Certain  groups 


2  Elementary  Chemistry 

of  facts  present  such  uniformity  of  relationships  as 
to  be  expressible  in  a  brief  statement  —  a  Law  of 
Nature.  Points  of  view  are  obtained  which  bring 
the  facts  and  the  laws  pertaining  to  them  into  such 
connection  that  the  labor  of  learning  them  is 
lightened.  The  contents  of  this  book  are  glean- 
ings from  the  work  of  many  men  of  many  countries 
throughout  many  years.  The  facts,  laws,  and  theo- 
ries are  presented  in  what  is  thought  to  be  the 
order  best  adapted  for  their  comprehension. 

3.  Matter  and  Energy.  Chemistry,  as  well  as 
all  other  so-called  physical  sciences,  has  to  do  with 
matter  and  energy.  Matter  may  be  denned  as  that 
which  occupies  space,  and  when  one  portion  of  matter 
does  ivork  upon  a  second,  it  is  said  to  possess  energy. 
We  get  our  knowledge  of  the  properties  of  matter 
through  the  medium  of  our  senses,  and  matter  can- 
not act  upon  our  senses  unless  it  possesses  energy. 
A  definite  portion  of  matter  is  called  a  body.  The 
kinds  of  matter  composing  bodies  are  called  sub- 
stances. Thus,  a  "lead"  pencil  is  a  body  made  up 
of  the  two  substances,  wood  and  "lead." 

The  amount  of  matter  in  a  body  is  called  its 
mass.  Two  bodies  are  said  to  have  equal  masses 
when  the  attraction  between  each  one  of  them  and 
a  third  body  is  the  same.  If  the  third  body  is  the 
earth,  the  attraction  is  called  gravity,  and  the  two 
bodies  are  said  to  have  the  same  weight.  Mass  is 
a  property  inherent  in  a  body  and-  is  independent 
of  other  bodies ;  weight  is  the  attraction  between 
bodies  and  the  earth.  Under  fixed  conditions  mass 
and  weight  are  proportional,  i.  c.,  they  increase  or 
decrease  in  the  same  way. 


Introductory  3 

4.  What  We  Study  in  Chemistry.  First  of  all, 
we  observe  the  properties  of  the  different  kinds  of 
matter.  Thus,  suppose  we  wish  to  make  a  chemical 
study  of  the  substance  known  as  roll  sulfur  or  brim- 
stone. By  our  sense  of  sight  we  learn  that  it  is  yel- 
low and  opaque ;  our  sense  of  touch  teaches  us  that 
it  is  brittle  and  rather  hard  ;  our  senses  of  taste  and 
smell  are  not  affected  by  it  and  we  hence  conclude 
that  it  is  tasteless  and  odorless.  We  further  ob- 
serve that  if  it  is  rubbed  against  a  piece  of  woolen 
cloth  it  will  attract  bits  of  paper  and  other  light 
substances ;  it  becomes  electrified,  we  say.  When 
we  heat  it  in  the  air,  it  melts,  takes  fire,  and  burns 
with  a  blue  flame  and  stifling  odor.  And  so  we 
could  go  on  accumulating  fact  upon  fact  and  thus 
increase  our  knowledge  of  sulfur.  By  appropriate 
experiments  we  can  in  a  similar  manner  get  a 
knowledge  of  every  other  substance. 

But  it  is  also  in  the  province  of  chemistry  to 
study  the  changes  and  transformations  that  sub- 
stances undergo.  Thus,  when  sulfur  burns  it  is 
completely  converted  into  a  gaseous  substance 
whose  most  striking  property  perhaps  is  its  sti- 
fling odor.  We  must  study  the  conditions  of  such 
changes  and  ascertain  what  other  substances  help 
in  bringing  about  the  changes.  Also,  the  energy 
manifested  as  heat  during  the  burning  of  sulfur, 
and,  in  general,  all  the  changes  of  energy  accom- 
panying changes  in  substances,  are  to  be  con- 
sidered. 

Further,  in  the  study  of  the  properties  and 
changes  of  substances,  certain  similarities  and  regu- 
larities are  sometimes  observed  whose  generalized 


4  Elementary  Chemistry 

statement  leads  to  the  Laws  of  Chemistry.  And 
man's  ingenuity  and  imagination  are  often  stimu- 
lated to  attempt  explanations  of  the  facts  discovered 
about  substances,  and  these  explanations  form  the 
hypotheses  and  theories  of  chemistry. 

5.  Physical  and  Chemical  Changes.  The  two 
metals,  platinum  and  magnesium,  behave  very 
differently  when  heated  in  the  air.  The  platinum 
may  become  hot  enough  to  emit  light,  but  when  it 
is  cool  it  assumes  its  original  appearance.  It  has 
undergone  only  physical  changes,  as  expansion  and 
incandescence.  When,  on  the  other  hand,  the 
magnesium  is  heated,  it  burns  with  a  dazzling  light 
and  is  changed  into  a  loose,  white  mass ;  a  chemical 
change  has  occurred. 

When  a  current  of  electricity  is  sent  through  a 
wire,  the  latter  is  heated,  and  with  strong  enough 
current  may  become  so  hot  as  to  glow  and  even  to 
melt.  But  when  a  current  of  electricity  passes 
through  a  solution  of  copper  sulfate  (blue  vitriol), 
the  solution  not  only  becomes  heated,  but  also 
copper  is  deposited  on  the  solid  by  which  the  cur- 
rent leaves  the  solution.  The  first  phenomenon 
is  an  example  of  a  physical,  the  second  of  a  chemical 
change. 

Experiments  similar  to  the  above  may  be  multi- 
plied almost  indefinitely.  They  all  go  to  show 
that  among  the  innumerable  changes  in  nature 
there  are  some  which  are  superficial  and  do  not 
bring  about  any  profound  alterations  in  the  sub- 
stances concerned,  while  there  are  others  in  which 
the  changes  are  considerable  and  deep-seated.  But 
there  are  also  many  changes  which  lie  between 


Introductory  5 

true  physical  and  chemical  changes,  and  the  dis- 
tinction is  often  but  slight  and  arbitrary.  Still,  it 
is  useful  and  hence  may  be  retained. 

6.  Physical    and    Chemical    Properties.      The 
properties  of  substances  studied  with   respect   to 
their  physical  changes  are  called  physical.     Impor- 
tant among  such  properties  are  color,   taste,  smell, 
hardness,  solubility,  etc.     Many  physical  properties 
can  be  expressed  numerically.    Thus,  an  important 
physical  property  of  a  substance  is  its  density — the 
mass  of  unit  volume  of  it.     For  example,  one  cubic 
centimeter  of  sulfur  weighs  2g-     The  density  of  sul- 
fur may  therefore  be  expressed  by  the  number  2. 
The  temperature  at   which   a   solid   turns   into   a 
liquid — its    melting  point — is    also    an    important 
physical   property;    likewise    the    temperature    at 
which  a  liquid  boils — the  boiling  point.    Such  numer- 
ical data  are  known  as  physical  constants. 

The  chemical  properties  of  substances  are  those 
involving  chemical  change.  Thus,  it  is  a  chemical 
property  of  sulfur  to  burn  with  a  blue  flame  and 
give  off  a  gas  of  stifling  odor. 

7.  The    Identification    of  Substances.     The 
number  of  properties  which  a  substance  may  have 
is  very  great,  and  the  question  arises :     How  many 
properties  of  a  substance  must  be  known  to  dis- 
tinguish it  from  every  other  substance?     Experi- 
ence  has    shown    that   if   samples    of    substances 
exactly  resemble  one  another  in  a  few  (a  half-dozen 
or  even  less)  properties,  they  will  resemble  one 
another  in  all  others.     This  simplifies  the  identi- 
fication of  substances  greatly,  and  it  is  one  of  the 
objects  of  chemistry  to  find  out  the  least  number 


6  Elementary  Chemistry 

of  properties  needed  to  identify  substances.  The 
identity  of  a  substance  is  established  by  means  of 
tests. 

8.  Tests.     By  subjecting  a   substance  to  the 
action  of  other  substances  under  certain  conditions 
and  comparing  the  results  with  known  and  recorded 
properties  we  make  a  test.     The  property  which  is 
most  characteristic -of  a  substance  is,  whenever  pos- 
sible, chosen  as  its  test.     Thus,  the  burning  of  sul- 
fur, with  its  blue  flame  and  stifling  odor,  is  ordinarily 
sufficient  to  establish  the  identity  of  that  substance. 
Additional  confirmatory  tests,  however,  are  usually 
employed  so  as  to  make  the  identification  surer. 
Thus,  the  color,  solubility,  and   electrification   of 
sulfur  may  be   employed  as   tests  to   confirm   its 
identity. 

9.  Chemical   Action.     Chemical    changes    are 
commonly  called  reactions.     The  substances  which 
react   are  called  reagents  or  factors,  and   the    sub- 
stances resulting  from  the  reaction,  products.    Chem- 
ical reactions  take  place  under  a  great  variety  of 
conditions.     Oftentimes  it  is  necessary  to  employ 
heat  or  electricity  —  sometimes  light  —  to  start  the 
reaction,  although  in  numerous  instances  the  mere 
bringing   together   of   the   reacting  substances   at 
ordinary  temperatures  is  sufficient.     It  is  seldom 
possible   to    bring   solid   substances   near   enough 
together  by  mere  mechanical  mixing  to  cause  the 
desired  reaction.    This,  however,  may  be  facilitated 
by  solution,  fusion,  pressure,  or  volatilization.     To 
ascertain   the   best  conditions  for   carrying   out  a 
reaction  is  one  of  the  most  important  tasks  that  the 
chemist  has  to  undertake. 


Introductory  7 

10.  The  Cause  of  Chemical  Change.    Why  cer- 
tain substances  when  brought  together  undergo  no 
great  change  even  when  heated,  while  others  react 
with  great  vigor  and  yield  products  of  totally  dif- 
ferent properties,  we  do  not  know.     The  cause  of 
chemical  change  is  hard  to  find.     We  can,  indeed, 
say  that  some  substances  have  a  "  chemical  affinity  " 
or  "  chemism  "  for  one  another,  but  this  really  does 
not  mean  much  and  explains  nothing.     Yet  just  as 
there  is  a  something  which  causes  all  portions  of 
matter  to  gravitate  towards  one  another,  so  is  there 
a  something  which   causes   certain   substances  to 
undergo  chemical  change  under  proper  conditions. 
While  we  are  at  present  unable  to  understand  what 
this  something  is,  still  we  can  try  to  ascertain  how 
it  acts ;  we  can,  at  least,  investigate  the  actions  and 
reactions  of  substances  upon  one  another. 

11.  Elements  and  Compounds.     The  diversity 
of  nature  is  infinite.     The  number  of  substances  is 
unlimited.     But  science  begins  with  classification. 
The  first  classification  of  chemistry  is  that  which 
divides  all  substances  into  elements  and  compounds. 
To  ascertain  whether  a  substance  is  an  element, 
chemists  proceed  as  follows :     They  take  a  definite 
weight  of  it  and  subject  it  to  all  possible  changes,, 
keeping  strict  account  of  the  weights  of  the  factors4 
and  products  in  all  the  reactions  studied ;  if  in  all 
these  changes  the  whole  of  it  has  not  been  converted 
into  another  substance  weighing  less  than  the  orig- 
inal  substance,   they   conclude   it    is   an   element. 
Thus,  iron  may  be  made  to  react  with  a  large  num- 
ber of  substances  to  give  rise  to  other  substances, 
not   one   of   which,   however,   has  been   found   to 


8  Elementary  Clicmistry 

weigh  less  than  the  iron  taken.     Iron  is  therefore 
an  element. 

An  element  then  is  a  substance,  a  given  weight 
of  which  has  never  all  been  changed  into  another 
substance  weighing  less  than  the  original.  All 
other  substances  are  composed  of  elements;  they 
are  called  compounds.  The  existence  of  nearly 
eighty  elements  has  been  established  ;  the  number 
of  compounds  is  limitless. 

NOTE.  Some  substances  which  were  at  one  time  supposed  to 
be  elements  have  later  been  found  to  yield  simpler  substances, 
and  it  is  quite  possible  that  some  of  the  elements  of  to-day  have 
no  right  to  the  name.  It.  should  be  borne  in  mind  that  the  term 
"element"  is  but  relative  and  depends  upon  the  state  of  our 
knowledge  and  skill. 

The  exact  number  of  elements  is  doubtful,  for  we  cannot  be 
sure  that  certain  substances  now  regarded  as  elementary  will  not 
ultimately  prove  to  be  compound,  and  also  because  but  a  relatively 
thin  layer  of  the  earth  has  been  subjected  to  examination. 

12.  Metals  and  Non-Metals.  It  has  been  found 
convenient  to  classify  elements  into  metals  and 
non-metals,  although  in  several  cases  it  is  difficult 
to  decide  to  which  class  an  element  belongs. 
Metals  have  a  peculiar  " metallic"  luster  and  are 
good  conductors  of  heat  and  electricity ;  they  are 
opaque  and  with  the  exception  of  mercury  are  solid 
under  ordinary  conditions ;  most  of  them  are  mal- 
leable and  ductile ;  i.  c.,  they  can  be  hammered  or 
rolled  into  sheets  and  drawn  out  into  wire.  Non- 
metals  do  not  have  a  "metallic"  luster  and  are  poor 
conductors  of  heat  and  electricity ;  several  of  them 
are  gaseous  under  ordinary  conditions.  The  chem- 
ical differences  between  metals  and  non-metals  will 
be  considered  in  connection  with  each  element. 


Introductory 


9 


METALS 

Aluminum 
Antimony 
Arsenic 
Barium 
Beryllium 
Bismuth 
Cadmium 
Caesium 
Calcium 
Cerium 
Chromium 
Cobalt 
Copper 
Erbium 
Gallium 
Germanium 
Gold 
Indium 
Iridium 
Iron 

Lanthanum 
Lead 
Lithium 
'Magnesium 
Manganese 


TABLE  OF  THE  ELEMENTS 

Mercury 

Molybdenum 

Neodymium 

Nickel 

Niobium 

Osmium 

Palladium 

Platinum 

Potassium 

Praseodymium 

Radium 

Rhodium 

Rubidium 

Ruthenium 

Samarium 

Scandium 

Selenium 

Silver 

Sodium 

Strontium 

Tantalum 

Tellurium 

Thallium 

Thorium 

Tin 

Titanium 


Tungsten 
Uranium 
Vanadium 
Ytterbium 
Yttrium     - 
Zinc 

Zirconium 
H  ^ 

NON-METALS 

Argon 

Boron 

Bromin 

Carbon 

Chi  or  in 

Fluorin 

Helium 

Hydrogen 

lodin 

Krypton 

Neon 

Nitrogen 

Oxygen 

Phosphorus 

Silicon 

Sulfur 

Zenon 


HISTORICAL  NOTE.  The  conception  of  an  element 
as  just  given  was  gained  towards  the  end  of  the 
eighteenth  century  and  is  mainly  due  to  the  French 
chemist,  Lavoisier.  Prior  to  that  time  it  was  held  that 
there  were  four  "elements" — fire,  water,  air,  and  earth 
—  and  that  the  properties  of  substances  depended  upon 
the  proportions  of  these  "elements"  which  they  were 
supposed  to  contain.  This  doctrine  dates  from  very 
ancient  times  and  was  arrived  at,  not  by  an  investi- 
gation of  nature  but  by  philosophical  speculation  alone. 
It  is  indeed  in  accord  with  a  superficial  view  of  phe- 
nomena, but  cannot  stand  the  test  of  a  stricter  scrutiny. 

i  The  more  important  elements  are  in  italics. 


io  Elementary  Chemistry 

For  example,  water  acted  upon  by  heat  (fire)  changes 
into  vapor  (air)  and  leaves  an  earthy  (earth)  residue. 
What  more  natural  than  to  conclude  that  water,  through 
fire,  changes  into  air  and  earth  ?  But  even  a  slight 
experimental  examination  shows  that  water  does  not 
cease  to  be  water  upon  vaporization,  for  the  vaporized 
water  may  be  condensed  again  into  the  liquid  form,  and 
also  that  the  earthy  residue  is  due  to  the  presence  of 
solid  substances  previously  dissolved  in  the  water. 

This  may  serve  as  an  instance  of  the  mode  of  reason- 
ing during  the  reign  of  the  four  elements.  When  men 
abandoned  speculation  and  entered  upon  thorough- 
going investigation,  endeavoring  to  account  for  every- 
thing in  a  phenomenon,  especially  the  changes  of 
weight,  the  progress  of  chemical  science  was  rapid. 

13.  Mixtures  and  Compounds.  Most  substances 
occurring  in  nature  are  made  up  of  several  others. 
Granite,  for  instance,  contains  three  or  more  differ- 
ent minerals.  If  the  constituents  of  a  substance 
can  be  separated  by  mechanical  processes,  as  by 
picking  them  out  or  dissolving  them  out,  they  are 
said  to  form  a  mixture.  If,  however,  mechanical 
processes  are  inadequate  in  effecting  a  separation, 
we  have  to  do  with  a  compound. 

ILLUSTRATIVE  EXAMPLE.  Mixtures  of  powdered  sulfur 
and  iron  may  be  prepared  in  all  proportions.  A  magnet 
stirred  about  in  the  mixture  will  pick  out  the  iron,  and 
a  liquid,  carbon  bisulfid,  will  dissolve  out  the  sulfur. 
These  means  of  separation  are  purely  physical,  and  we 
have  to  do  with  a  mixture.  When  a  mixture  of  fifty-six 
parts  by  weight  of  iron  and  thirty-two  parts  of  sulfur  is 
heated  in  a  flame  it  begins  to  glow  at  a  certain  temper- 
ature, and  enough  heat  is  evolved  to  keep  the  mixture 
incandescent  for  some  time,  even  after  the  flame  is  re- 
moved. A  chemical  change  has  taken  place.  We  now 
find  on  applying  the  magnet  and  the  carbon  bisulfid  that 
the  product  is  much  less  magnetic  and  nearly  insoluble. 
A  compound  of  iron  and  sulfur  has  been  formed. 


Introductory  \  i 

14.  Differences  Between  Mixtures  and  Com- 
pounds.    In  the  preparation  of  mixtures  but  little 
energy,  and  that  mechanical,  is  required,  while  in 
the    preparation    of    compounds    the    changes    of 
energy  are  considerable.     Also  the  properties  of  a 
mixture  are  about  the  average  of  the  properties 
of  its  constituents.     But  the  compound  usually  has 
totally  different  properties  from  those  of  the  ele- 
ments composing  it.     There  is  ordinarily  as  much 
difference  between  the  compound  and  each  one  of 
its  constituents  as  there  is  between  the  elements 
themselves   entering   into   its   composition.     This 
profound  alteration  of  properties  is  characteristic 
of   a   chemical   change.     Further,  compounds   are 
characterized  by  having  an  invariable  composition. 
Only  so  much  sulfur  can  combine  with  so  much 
iron,  tod  an  excess  of  either  element  present_dpes 
not  en'ter  into  reaction.     To  ascertain  as  accurately 
as  possible  what   these  combining  proportions  of  tJic 
elements  are  is  one  of  the  fundamental  problems  of 
chemistry. 

To  sum  up,  compounds  differ  from  mixtures  in 
that: 

/.  They  have  constant  physical  properties  dif- 
ferent from  those  of  their  constituent  elements. 

2.  Not  inconsiderable  amounts  of  heat  or  other 
forms  of  energy  are  made  manifest  in  their  forma- 
tion. 

j.     They  have  an  invariable  composition. 

15.  Conservation  of  Matter  and  Energy.    The 
chemical  and  physical  changes  of   substances   in- 
volve primarily  changes  of  mass  and  energy.     It 
has  been  found  that  even  in  the  most  complicated 


12  Elementary  Chemistry 

changes,  if  strict  account  be  kept  of  all  the  amounts 
of  matter  and  energy  that  undergo  transformation, 
these  always  foot  up  to  the  same  sum  total.  Neitlier 
matter  nor  energy  can  be  created  or  destroyed. 

These  facts  of  experience  have  led  to  the  estab- 
lishment of  two  grand  laws  which  pervade  all 
the  physical  sciences:  the  Law  of  the  Conservation 
of  Energy  and  the  Law  of  the  Conservation  of 
Matter.  These  twTo  laws  are  of  fundamental  im- 
portance and  apply  to  every  physical  and  chemical 
change. 

16.  The  Immutability  of  the  Elements.  While 
there  are  about  eighty  elementary  kinds  of  matter, 
there  are  only  a  half-dozen  or  so  of  different  kinds 
of  energy,  as  mechanical,  chemical,  electrical,  etc. 
These  different  kinds  of  energy  may,  with  certain 
restrictions,  be  converted  into  one  another.  Such 
is  not  the  case,  however,  with  the  different  kinds  of 
elementary  substances.  While  mechanical  energy 
may  be  converted  into  electrical  or  heat  energy, 
lead  or  copper  cannot  be  changed  into  gold. 

This  immutability  of  the  elements  has  not 
always  been  recognized ;  indeed,  up  to  the  end  of 
the  eighteenth  century  one  of  the  principal  aims 
of  chemistry  (or  alchemy,  as  it  was  then  called) 
was  to  devise  means  to  convert  cheap  materials 
into  the  valuable  metals,  silver  and  gold. 

HISTORICAL  NOTE.  To  Lavoisier  belongs  the  credit 
of  having  been  the  first  clearly  to  enunciate  and  vigor- 
ously to  emphasize  the  Law  of  the  Conservation  of 
Matter.  The  Law  of  the  Conservation  of  Energy 
was  not  stated  until  a  little  more  than  a  half-century 
later,  when  Mayer,  Helmholtz,  and  Joule  announced  it 
independently. 


Introductory  1 3 

IMPORTANCE  OF  CHEMISTRY.  Chemistry  has  not  only 
great  value  as  a  means  of  mental  discipline,  but  also 
great  usefulness  in  supplying  the  needs  of  man.  By 
its  aid  many  products  which  were  formerly  thrown 
away  are  now  rendered  useful,  and  its  discoveries  are 
now  applied  to  practical  use  in  medicine,  agriculture, 
and  in  nearly  every  great  manufacturing  industry. 
Chemistry  is  also  a  fundamental  science  upon  which 
certain  other  sciences,  as  biology,  physiology,  and  min- 
eralogy, are  to  a  considerable  extent  based. 

Exercises 

/.     How  would  you  make  a  chemical  study  of  coal  ? 

2.  State  the  kind  of  change  in  each  of  the  following :  (a)  the 
burning  of  wood,  (b*)  the  melting  of  ice,  (c)  the  welding  of  iron, 
(<tf)the  rusting  of  iron,  (e)  the  tarnishing  of  silver. 

j>.  Give  as  many  physical  and  chemical  properties  as  you 
can  of  the  following  substances :  Gold,  silver,  lead,  tin,  copper. 

4.  Which  of  the  properties  found  in  answer  to  the  previous 
exercise  will  best  serve  as  tests  ? 

5.  How  have  chemists  come  to  the  conclusion  that  iron  is  an 
element? 


CHAPTER  II 

THE  GENERAL  PROPERTIES  OF  GASES 

17.  States  or  Conditions  of  Matter.  Any  defi- 
nite kind  of  matter  can  be  made  to  assume  three 
more  or  less  clearly  defined  states,  merely  by  the 
alteration  of  the  relative  amounts  of  energy  it  con- 
tains in  the  form  of  heat.  Thus,  water  may  be 
converted  into  ice  by  the  withdrawal  of  heat,  and 
into  steam  by  the  addition  of  heat;  the  freezing 
and  boiling  of  water  take  place  under  fixed  con- 
ditions of  temperature  and  pressure.  In  general, 
then,  a  substance  may  be  obtained  in  the  solid, 
liquid,  or  gaseous  state  by  suitable  adjustment  of 
temperature  and  pressure,  and  it  is  the  relative 
amount  of  heat  energy  contained  in  it  which  de- 
termines its  state  of  aggregation. 

A  solid  has  a  definite  shape  and  a  definite  volume. 

A  liquid  has  a  definite  volume,  but  takes  the  shape 
of  the  vessel  containing  it.  Its  free  surface,  i.  e., 
the  surface  not  in  contact  with  a  solid,  is  horizontal. 

A  gas  has  neither  shape  nor  volume  of  its  own  ;  these 
depend  upon  the  shape  and  the  volume  of  the  con- 
taining vessel.  A  gas  spreads  out  and  fills  any 
space  offered  it. 

A  rise  of  temperature  has  the  same  effect  upon 
matter  in  all  three  states ;  with  but  few  exceptions 
substances  increase  in  volume  when  heated.  Solids 
change  the  least,  liquids  more,  and  gases  most. 
Also,  an  increase  of  pressure  diminishes  the  vol- 
ume of  substances  in  all  three  states. 

[14] 


The  General  Properties  of  Gases  15 

18.  The  Necessity  for  a  Preliminary  Study  of 
Gases.     We  know  far  more  about  the  gaseous  state 
than  about  the  liquid  or  solid  states,  and  chemistry 
is  to  a  large  extent  built  upon  facts  derived  from 
the  study  of  gases.    As  the  first  elements  we  shall 
study  are  gases  and  form  gaseous  or  volatile  com- 
pounds, it  is  necessary  that  we  acquire  beforehand 
a   knowledge   of   the  general  properties  of  gases. 
This  belongs  properly  to  the   subject  of  physics, 
but  it  is  so  necessary  fora  comprehension  of  chem- 
istry that  it  must  also  be  given  here. 

19.  Volume,  Pressure,  and   Temperature.     In 
chemistry,  volumes  are  measured  usually  in  cubic 
centimeters  (c- c-)  or  in  liters  (/-).'    (See  Appendix  B.) 

Pressures  are  measured  in  atmospheres  or  in 
millimeters  (»"«•)  of  mercury.  The  air  presses 
down  upon  the  earth's  surface  on  an  average  so  as 
to  balance  at  the  level  of  the  sea  a  vertical  column 
of  mercury  760"""-  high,  and  this  pressure  is  defined 
to  be  the  standard  pressure  of  one  atmosphere. 

Temperatures  are  measured  by  mercury-in-glass 
thermometers  graduated  according  to  the  centi- 
grade scale.  (See  Appendix  C.)  The  zero  cor- 
responds to  the  temperature  of  melting  ice  and  the 
1 00°  point  to  the  temperature  of  water  boiling  under 
standard  pressure.  The  one  hundredth  part  of  this 
fundamental  interval  is  set  equal  to  one  degree, 
and  the  value  of  a  degree  thus  determined  is 
extended  above  and  below  these  fixed  points. 

20.  Charles'  Law.     All  gases  under  constant  pres- 
sure expand  equally  for  like  changes  of  temperature. 

Thus,  it  has  been  found  that  one  liter  of  a  gas 
measured  at  o°  becomes : 


1 6  Elementary  Chemistry 

(i  +      -)  liters  at  i°;    (i  +  -   -)  liters  at  2°; 
273  273 

(i  +  — )  liters  at  3°;    (i  -f-  — )  liters  at  4°; 

273  273 

(i  +  — )  liters  at  5°;    (i  +  — )  liters  at  t°\ 

273  273 

and 

i  2 

(i  -        -)  liters  at  — 1°;    (i  -        -)  liters  at  —2°; 
273  273 

(i — )  liters  at  —3°;    (i )  liters  at  —t°. 

273  273 

21.  Absolute  Temperatures.  A  given  mass  of 
any  gas  which  at  o°  occupies  273  c-c-  will  have  at 
100°  a  volume  of  (273  +  100)  =  373  c-c-,  and  at  —  ioo°a 
volume  of  (273  — i oo)  =  ij$c-c-.  At —273°,  therefore, 
the  volume  of  the  gas  would  be  (273  —  273)  =  oc-c-, 
i.  e.,  it  would  be  reduced  to  nothing.  Such  a  con- 
clusion is  manifestly  absurd,  and,  as  a  matter  of 
fact,  all  gases  are  condensed  into  liquids  and  solids 
before  such  a  low  temperature  is  reached.  If 
—273°  be  taken  as  a  starting  point  and  the  centi- 
grade value  of  a  degree  be  retained,  a  therm ometric 
scale  will  be  obtained  on  which  the  readings  are 
directly  proportional  to  the  volumes  of  the  gas. 
Such  a  scale  is  called  the  absolute  scale,  and  —273° 
is  known  as  the  absolute  zero.  Centigrade  readings 
of  temperature  are  converted  into  absolute  read- 
ings by  adding  273  to  the  former,  thus: 

273°   (absolute]   =      o°  (centigrade), 

274°  "          =1° 

270°          "          =  -3°  »  etc. 


LA  VO1SIER 


PRIESTLEY 


SCHEELE 


CA  VEX  DISH  BLACK 

Plate  II 


CARL  WILHELM  SCHEELE  ANTOINE  LAURENT  LAVOISIER 
1742-1786 ;  Swede  1743-1794;  French 

Discovered  oxygen,  chlorin,  am-  Showed  role  oxygen  plays  in  com- 

monia,    manganese,    and    many  bustion  phenomena.    Propounded 

acids.     Devised  methods  of  prep-  the  Law  of  the  Conservation  of 
arationfor  many  substances  Matter 


JOSEPH  PRIESTLEY 

1733-1804;  English 

Discovered  oxygen  and  several 
other  gases.  Devised  metJiods 
for  handling  and  storing  gases 


JOSEPH  BLACK  HENRY  CAVENDISH 

1728-1799;  English  1731-1810;  English 

First  prepared  carbon  dioxid  in  Discovered  hydrogen  and  compo- 

isolated  state.    Introduced  more  sition    of   ivater.        Defer  mined 
definite  notions  about  gases  composition  of  the  air 


Plate  II 


The  General  Properties  of  Gases  17 

22.  Boyle's  Law.     If  the  temperature  of  a  gas  be 
maintained  constant,  its  volume  varies   inversely  as  its 
pressure. 

Thus,  if  the  pressure  is  doubled,  the  volume  is 
half  as  large ;  if  the  pressure  be  reduced  to  one- 
third,  the  volume  is  trebled,  and  so  on. 

23.  Density  and  Specific  Gravity.     The  density 
of  a  substance  is  the  mass  of  unit  volume  of  it ;  its 
specific  gravity  is  the  ratio  of  the  weight  of  a  given 
volume  of  it  to  the  weight  of  an  equal  volume  of 
another  substance  taken  as  a  standard.  'Two  stand- 
ards are  in  use  for  gases. — air  and  hydrogen  —  while 
water  is  the  standard  for  liquids  and  solids.     The 
weights  of  one  liter  of  hydrogen  and  of  air  at  o°  and 
760  mm-  of  mercury  are  0.09^-  and    1.293^-   respec- 
tively.    With   hydrogen   as   standard,  the  specific 
gravity  of  air  is  1.293/0.09=  14.37,  while  with  air 
as   standard,  the   specific   gravity  of   hydrogen   is 
0.09/1.293  =0.069. 

NOTE.  It  is  unfortunate  that  two  standards  are  in  use.  Hydro- 
gen is  the  standard  used  in  this  book,  and,  unless  stated  to  the 
contrary,  specific  gravities  will  be  referred  to  hydrogen. 

The  term  vapor  density  is  often  used  to  distinguish  the  specific 
gravity  of  a  substance  in  the  gaseous  or  vaporous  state  from 
that  which  it  may  have  in  the  liquid  or  solid  condition. 

24.  Standard   Conditions.     When  the  weights 
of  a  liter  of  air  and  of  hydrogen  were  given  (§23) 
both  the  temperature  and  the  pressure  were  speci- 
fied.    This  is  necessary  in  all  cases,  for  the  volume 
that  a  given  mass  of  gas  occupies  depends  upon 
its  pressure  and  temperature.     In  comparing  the 
weights  of   the   volumes  of  gases,   both  the   tem- 
perature and  pressure  must  be  stated,  or  at  least 


1  8  Elementary  Chemistry 

understood.  Chemists  have  agreed  to  give  the 
weights  of  gases  with  their  volumes  at  the  standard 
temperature  of  o°  (273°  on  the  absolute  scale)  and 
at  the  standard  pressure  of  one  atmosphere.  The 
reduction  of  the  volumes  of  gases  measured  at 
other  temperatures  and  pressures  than  these  stand- 
ard conditions  may  be  effected  by  the  application 
of  the  laws  of  Boyle  and  Charles.  They  may  be 
applied  separately  or  in  combination. 

25.  Reduction  of  the  Volume  of  a  Gas  to  Stand- 
ard Pressure.  Suppose  we  have  v  liters  of  a  gas 
under  a  pressure  of  /  mm-  of  mercury,  and  wish  to 
find  its  volume  v'  at  760  mm-  of  mercury.  Boyle's 
Law  permits  us  to  write  the  proportion  : 


v         760 

v'         p 

Whence, 

760  v'  —  p  v 

and 

760 

In  words :  To  reduce  the  volume  of  a  gas  to  stand- 
ard pressure,  multiply  the  given  volume  by  a  fraction 
whose  denominator  is  always  J$o  and  whose  numerator 
is  the  given  pressure. 

26.  Reduction  of  the  Volume  of  a  Gas  to  Stand- 
ard Temperature.  Suppose  v^  liters  of  a  gas  to 
have  been  measured  at  the  temperature  of  /°,  and 
that  it  is  required  to  find  its  volume,  v\  at  o°,  /.  e., 
273°  on  the  absolute  scale.  By  Charles'  Law  we 
have: 


273 


The  General  Properties  of  Gases  19 

Whence, 

(273  +  0  v\  =  273  V* 

aM  273 


273  +  ^ 

In  words :  To  reduce  the  volume  of  a  gas  to  standard 
temperature,  multiply  the  given  volume  by  a  fraction 
whose  numerator  is  always  273  and  whose  denominator 
is  273  plus  the  given  temperature,  i.  e.,  the  absolute  tem- 
perature. 

27.  Reduced  Volumes.  This  is  an  elliptical 
expression  for  volumes  reduced  to  o°  and  760  mm- 
of  mercury.  As  Boyle's  and  Charles'  Laws  are 
independent  of  each  other,  the  reductions  to  stand- 
ard conditions  maybe  made  independently;  that  is, 
we  may  suppose  the  pressure  constant  and  reduce 
to  standard  temperature,  and  then  suppose  the  tem- 
perature constant  and  reduce  to  standard  pressure. 
But  these  reductions  may  be  combined  in  one 
expression.  If  v  denote  the  volume  of  a  gas  at  t° 
and  p  mm-  of  mercury,  the  reduced  volume  V  may 
be  found  by  means  of  the  formula : 

P      273 


760  273+  / 

or 


760  273+/ 


1  This  formula  is  derived  as  follows  : 
By  Boyle's  Law, 

i 
v  x>  — ,  where   T  ( absolute  scale}  is  constant; 


2O  Elementary  Chemistry 

Whence  the  rule : 

To  reduce  a  given  volume  of  gas  to  standard  condi- 
tions, multiply  it  by  273/760  (=0.350)  and  a  fraction 
w/iose  numerator  is  the  given  pressure  and  whose  denomi- 
nator is  the  absolute  temperature. 

NOTE.  If  the  volume  of,  a  gas  at  a  certain  temperature  and 
pressure  is  to  be  found  at  any  other  temperature  and  pressure 
than  o°  and  760  tnm.t  only  the  fraction  273/760  needs  to  be 
changed  ;  its  numerator  is  made  equal  to  the  given  absolute  tem- 
perature and  its  denominator  to  the  given  pressure. 

Also  sometimes  the  volume  of  a  gas  under  standard  conditions 
is  known  and  it  is  required  to  find  the  volume  it  occupies  at  a 
certain  stated  temperature  and  pressure.  In  such  cases  the  known 
volume  for  V  is  substituted  in  the  formula  and  the  unknown 
volume  v.  calculated. 

and  by  Charles'  Law, 

v  DO  T,  when^  is  constant. 
Combining  the  two  expressions, 

T       vp 
v  X)  — ,  or  —  —  a  constant  quantity. 

For  an  equal  weight  of  the  same  gas  under  different  conditions 
of  temperature,  pressure,  and  volume,  denoted  by  T  ,  p' ,  and  v',. 
a  similar  expression  is  true: 

v-  p' 

-=7  =  a  constant  quantity; 

and  as  the  weight  of  the  gas  does  not  change,  the  constant  quan- 
tity is  the  same  in  both  cases,  so  that 


T'         T 
and 

P      T' 


'    T 

where  if  v'  (~V)  denote  the  volume  at  o°  C.  and  760  »"».,  T'  -- 
273,  P  =  760,  and  T  =  273  +  /  .• 

273          p 
760     273  +  / 


The  General  Properties  of  Gases 


MODES  OF  MEASURING  GASES.  A  common  mode  of 
measuring-  the  volume  of  a  gas  is  the  following":  A 
graduated  tube  (Fig.  i),  closed  at  one  end,  is  filled  with  a 
liquid,  usually  water 
or  mercury,  closed 
with  the  thumb,  a 
cork,  or  a  glass  plate, 
inverted  and  opened 
with  its  mouth  below 
the  surface  of  the 
liquid,  which  is  con- 
tained in  a  vessel  or 
dish  commonly  called 
a  pneumatic  trough. 
By  means  of  a  deliv- 
ery tube  the  gas  is 
then  made  to  bubble 
up  into  the  tube  and 
displace  the  liquid.  If 
the  pneumatic  trough 
is  deep  enough  to  per- 
mit of  the  tube  being 
raised  or  lowered  so 
that  the  level  of  the 
liquid  inside  and  out- 
side of  the  tube  may 
be  made  the  same,, 
the  pressure  of  the 
confined  gas  is  equal 
to  that  of  the  atmos- 
phere, as  read  from 
a  barometer,  and  its 
volume  is  given  by  the 
reading  on  the  tube 
at  the  level  of  the 
liquid.  If  the  trough 
is  not  deep  enough 
for  this,  the  pressure 
of  the  enclosed  gas 
will  be  less  than  that  of  the  atmosphere,  since  the  atmos- 
phere has  to  support  the  column  of  liquid  in  the  tube 
above  the  level  of  the  liquid  in  the  pneumatic  trough. 


Fig.   I — GAS-MEASURING  TUBE  AND  MERCURY 
PNEUMATIC  TROUGH 

The  wires  leading  to  the  top  of  the  tube  connect 

with  platinum  wires  fused  in  the  glass.     Such  a 

tube  is  a  eudiometer  (§  50) 


22  Elementary  Chemistry 

Hence,  to  find  the  actual  pressure  exerted  by  the 
gas,  the  vertical  distance  between  the  surfaces  of  the 
liquid  inside  and  outside  of  the  tube  is  measured.  If 
the  liquid  be  mercury,  this  distance  is  subtracted  from 
the  barometric  reading,  and  the  remainder  is  the  pres- 
sure of  the  gas.  If  any  other  liquid  is  used,  the  pressure 
of  the  column  of  liquid  must  be  reduced  to  millimeters 
of  mercury  by  multiplying  it  by  a  fraction  whose  num- 
erator is  its  specific  gravity  and  whose  denominator  is 
the  specific  gravity  of  mercury,  both  referred  to  water 
as  standard.  If  h  denote  in  millimeters  of  mercury  the 
pressure  of  the  column,  the  formula  for  the  reduction 
of  gas  volumes  becomes : 

F'=W273     P~k\ 
\  760  273+?  j 


VOLUME  MEASUREMENTS  BY  MEANS  OF  WEIGHT 
MEASUREMENTS.  The  fact  that  one  cubic  centimeter 
of  water  weighs  one  gram1  renders  it  possible  to  find 
volumes  by  means  of  weight  measurements.  Thus, 
if  the  volume  of  a  gas,  measured  as  just  described, 
but  with  an  ungraduated  tube,  be  marked  on  the  con- 
taining vessel  with  a  rubber  band,  piece  of  gummed 
paper,  etc.,  the  weight  of  the  water  filling  the  inverted 
vessel  up  to  this  mark,  if  expressed  in  grams,  may  be 
taken  as  the  volume  of  the  gas  in  cubic  centimeters. 

28.  Correction  for  Vapor  Tension.  When  the 
liquid  over  which  a  gas  is  collected  is  somewhat 
volatile  at  the  temperature  of  the  measurement,  a 
correction  to  the  pressure  has  to  be  applied.  Thus, 
a  gas  collected  over  water  is  permeated  with  water 
vapor,  for  water  sends  off  vapor  at  all  tempera- 
tures. This  vapor,  just  like  a  gas,  exerts  a  pressure 
or  tension  which  opposes  the  pressure  of  the  atmos- 
phere as  measured  by  the  barometer  and  is  greater 

1  This  is  strictly  true  only  at  4°.  Its  approximation  to  truth, 
however,  is  close  enough  for  all  purposes  of  our  measurement  of 
the  volumes  of  gases  at  ordinary  temperatures. 


The  General  Properties  of  Gases  23 

the  higher  the  temperature.  According  to  Dalton's 
Law: 

Each  gas  or  vapor  present  in  a  mixture  of  gases  or 
vapors  exerts  the  same  pressure  as  it  would  if  it  alone 
iv ere  present,  or,  in  other  words,  the  pressure  of  a 
gaseous  mixture  is  the  sum  of  the  partial  pressures  of  its 
components. 

Hence,  to  find  the  pressure  exerted  by  a  gas 
alone,  the  pressure  due  to  the  vapor  of  the  liquid 
must  be  subtracted  from  the  total  pressure  of  the 
gaseous  mixture  as  given  by  reading  of  the  barom- 
eter. The  formula  for  reduction  to  standard  con- 
ditions must  then  receive  a  further  correction  and 
reads,  if  p'  denote  the  pressure  of  the  vapor  of  the 
liquid : 

V"  =  v  (  273  P—h—P 
\  760    273  +  t 

The  tension  of  water  vapor  as  measured  at  ordi- 
nary temperatures  is  given  in  Table  II.  (See 
Appendix  D.} 

Problems 

/.    What  is  the  volume  at  760  mm.  of  mercury  of  301.7  c.c.  of  a 
gas  measured  at  750  mm.  ? 
Solution : 
Calling  the  required  volume  v'  we  have  : 

301.7  _    760 
V       '    750 
Whence, 

V  =  301. 7-^-  =  297-7  c-c- 

2.     What  is  the  volume  under  standard  pressure  of  : 

(a)  728  c.c.  of  gas  measured  under  1,829  mm-  °f  mercury? 

(b)  63  /•  of  gas  measured  under  378  mm.  of  mercury  ? 

(c)  28  /•  of  gas  measured  under  17.6  atmospheres  ? 

(d)  846  c.c.  of  gas  measured  under  0.738  atmospheres  ? 


24  Elementary  Chemistry 

j.     What  is  the  volume  at  o°  of  326  c.c.  of  gas  measured  at  22°  ? 

Solution  : 

Denoting  the  required  volume  by  v\,  we  have  : 

326  _  273  +  22 

Vi   ~         273 

Whence,  v'    —  326  2-^  =  301.1  c.c. 

295 

./.     What  is  the  volume  at  standard  temperature  of  : 
(«)    935-6  c.c.  of  gas  measured  at  ioo°? 

(b)  26.4^-  of  gas  measured  at  —  io°? 

(c)  492.8^-  of  gas  measured  at  84°? 
(d}    624.4  c.c.  of  gas  measured  at  62°? 

j-.     What  is  the  reduced  volume  of  256  c.c.  of  a  gas  measured  at 
C6o  mm.  and  27°? 
So  hit  ion  : 
Substituting  in  the  general  formula,  we  have  : 

^ 


76o  273 

6.  What  is  the  volume  under  standard  conditions  of  74  /•  of 
gas  measured  at  ge,omm.  and  197°? 

7.  Reduce  to  standard  conditions  : 

(a)     14  c-c-  of  gas  measured  at  763  mm-  and  —  11°. 
(b}     6.2  c.c.  of  gas  measured  at  m  mm.  and  27°. 
(c)     279  c.r-  of  gas  measured  at  725  mm.  and  17°  . 

8.  A  vessel  20  cm.  long,  io«»-  wide,  and  $cm.  deep  is  filled 
with  air  at  "jgomm-  and  35°.     What  is  the  volume  under  standard 
conditions? 

q.  A  gas  volume  measures  15.1  c.c.  at  o°  and  760  mm.  What 
is  its  volume  at  goo  mm.  and  17°? 

10.  If  654  c.c.  of  gas  are  measured  at  16°  and  734  ;«»/.,  what 
is  the  volume  at  35°  and  895  mm.? 

n.  The  volume  of  a  gas  measured  in  a  graduated  tube  over 
mercury  was  found  to  be  93  c.c.,  the  temperature  being  17°,  and  the 
height  of  the  barometer  738^^-  The  level  of  the  mercury  inside 
the  tube  was  i%mm.  higher  than  that  in  the  trough.  What  would 
be  the  volume  of  the  gas  under  standard  conditions  ? 

Solution  : 

Substituting  in  the  formula,  we  have  : 

F'=93fe   738  -78\  _ 

\76o  273  +  17; 


TJie  General  Properties  of  Gases  25 

12.  A  gas  was  measured  over  water  (and  hence  was  saturated 
with  water  vapor)  at  20°  and  744  >«>»•,  and  was,  found  to  have  a 
volume  of  628  c.c.,  when  the  levels  of  the  water  inside  and  outside 
of  the  vessel  were  the  same.  What  would  its  volume  be  under 
standard  conditions? 

Solution  : 

The  tension  of  aqueous  vapor  at  20°  is  ij.^mm.  of  mercury 
and  substituting  in  the  formula  we  have  : 

V"=  628  fe3  744-!7.4\ 
\j6o  273  +  20    ) 

7j>.  Reduce  to  standard  conditions  937 c.c,  of  gas  saturated 
with  water  vapor  at  24°  and  621  mm. 

14.  Reduce  to  standard  conditions  76^-  of  a  gas  saturated 
with  water  vapor  at  21°  and  763  tnm.t  when  the  difference  of  the 
water  levels  inside  and  outside  the  vessel  containing  the  gas  was 
439 ;«;«.  (The  specific  gravity  of  mercury  referred  to  water  is  13.6.) 

75.  i^bc.c.  of  air  at  23°  and  746 mm.  of  mercury  were  measured 
over  water.  What  volume  would  the  dry  gas  occupy  at  o°  and 
760  mm.~) 

16.  If  a  certain  mass  of  gas  measures  300  c.c.  when  the  barom- 
eter stands  at  760  mm.y  and  later  contracts  to  297  c.c.t  what  is  the 
barometer  reading  corresponding  to  the  latter  volume? 

77.  If  a  gas  under  standard  conditions  has  its  pressure 
doubled  and  its  temperature  raised  until  the  volume  is  the  same 
as  its  original  volume,  what  is  its  final  temperature? 

1 8.  What  is  the  reduced  volume  of  77.7^-  of  air  saturated 
with  water  vapor,  if  measured  at  17.5°  with  the  barometer  at 
755-5  mm-,  the  aqueous  tension  being  14.9  w«.? 

79.  Reduce  to  standard  conditions  1,328^-  of  gas  saturated 
with  water  vapor  and  measured  under  the  following  conditions  : 
Pressure,  765  #*>«.;  temperature,  18°;  aqueous  tension,  15.4."""- 

20.  What  volume  under  standard  conditions  would  be  occu- 
pied by  200  c.c.  of  gas  at  14°  and  756  mm."> 

21.  If  a  certain  mass  of  air  occupies  140^-  when  the  tempera- 
ture is  27°  and  the  height  of  the  barometer  750™"*-,  wrhat  will  its 
volume  be  when  the  temperature  is  9°  and  the  barometer  reading 
770  mm.') 

22.  What  is  the  volume  of  1,520^-  of  hydrogen  measured  at 
54°  with  the  barometer  at  780  ?«™.  if  the  temperature  and  barom- 
eter change  to  18°  and  740  »«'«•? 


CHAPTER    III 


OXYGEN  AND  OZONE 

OXYGEN 

HISTORICAL  NOTE.  Oxygen  was  first  isolated  by 
the  Englishman,  Priestley,  in  1774  ;  also  independently 
by  the  Swede,  Scheele,  a  few  months  later.  Its  dis- 
covery attracted  much  attention.  Lavoisier,  in  1778, 
showed  the  important  part  it  plays  in  the  phenomena  of 
combustion,  and  gave  it  the  name  of  oxygen.  Previous 
to  that  time  it  had  been  called  vital  air,  dephlogisticated 
air,  and  the  eminently  respirable  air. 

29.  Occurrence.  Oxygen  is  the  most  abundant 
of  all  the  elements.  More  than  a  fifth  of  the  atmos- 
phere consists  of  free  or  uncombined  oxygen.  In 
combination  with  other  elements  it  forms 
nearly  50  per  cent  of  the  weight  of  the 
earth's  crust.  Water  contains 
88. 8 1  per  cent  of  it,  and  it  is  a 
constituent  of  most  animal  and 
vegetable  substances. 

30.  Preparation.  Al- 
though oxygen  occurs  un- 
combined in  the  atmosphere, 

.  2 APPARATUS    FOR    PREPAR-          .         . 

ING  OXYGEN  BY  FOCUSING  THE  it  IS  difficult  tO  free  it  frOHl 
SUN  S  RAYS  ON  RED  PRECIPITATE 

the  other  atmospheric  gases, 

at  least  on  a  small  scale.  The  usual  way  to  prepare 
it  is  to  heat  certain  of  its  compounds.  Thus,  mer- 
curic oxid  (red  precipitate),  silver  oxid,  manganese 
dioxid  (black  oxid  of  manganese),  potassium  chlorate 
(chlorate  of  potash),  and  several  other  compounds 

[26] 


Oxygen  and  Ozone 


27 


Fig.  3 — PREPARATION  OF  OXYGEN   BY 'HEATING  A  MIXTURE  OF  POTASSIUM  CHLO- 
RATE AND  MANGANESE  DIOXID  IN  A  RETORT 

yield  oxygen  when  heated.  Its  preparation  from 
red  precipitate  is  historically  interesting  because 
Priestley  first  prepared  the  gas  in  a  state  of  purity 
by  using  a  lens  to  focus  the  sun's  rays  upon  the 
compound.  (Fig.  2.) 

A  mixture  of  potassium  chlorate  and  manga- 
nese dioxid  gives  off  oxygen  much  more  readily 
when  heated  than  does  either  of  these  compounds 
when  heated  alone.  (Fig.  3.)  While  the  potassium 
chlorate  is  thus  converted  into  potassium  chlorid  and 
oxygen,  the  manganese  dioxid  does  not  seem  to  be 
at  all  changed.  It  helps  along  the  reaction  in  some 
as  yet  unexplained  way,  without  itself  undergoing 
any  permanent  change. 

CATALYSIS.  There  are  numerous  cases  similar  to 
this.  Generally  speaking,  when  the  addition  of  a  sub- 
stance causes  a  reaction  to  take  place  between  other 
substances,  or  alters  the  conditions  of  the  reaction,  as 


28  Elementary  Chemistry 

its  speed  or  the  temperature  at  which  it  starts,  and  does 
not  itself  become  permanently  changed,  such  a  sub- 
stance is  said  to  exercise  a  catalytic  action,  and  the 
process  is  known  as  catalysis. 

OTHER  MODES  OF  PREPARATION.  Oxygen  may  also 
be  prepared  by  passing  a  current  of  electricity  through 
a  solution  of  copper  sulfate,  by  the  action  of  water  on 
sodium  peroxid,  by  the  interaction  of  nitric  acid,  red 
lead,  and  potassium  permanganate,  by  the  action  of 
cobalt  nitrate  on  a  mixture  of  bleaching  powder  and 
water,  and  by  many  other  reactions.  When  liquid  air 
evaporates,  its  oxygen,  being  less  volatile,  does  not  boil 
away  as  rapidly  as  the  other  main  constituent,  so  that 
finally  the  liquid  consists  of  over  90  per  cent  of  oxygen, 
which  is  pure  enough  for  many  industrial  purposes. 

31.  Properties.  (Table!.,  Appendix  D.}  Phys- 
ical. Oxygen  is  a  colorless,  odorless,  and  tasteless 
gas,  but  slightly  soluble  in  water  and  other  liquids. 
It  is  the  most  magnetic  of  all  the  gases.  Liquid 
oxygen  has  a  light  blue  color. 

Chemical.  It  forms  compounds  with  nearly  all 
the  elements.  With  some  elements,  notably  phos- 
phorus and  potassium,  union  takes  place  at  ordinary 
temperatures,  but  usually  it  is  necessary  to  raise 
the  temperature.  The  union  of  oxygen  with  other 
substances  is  commonly  called  oxidation,  but  when  a 
substance  combines  with  oxygen  so  as  to  give  off 
light  and  heat,  it  is  said  to  burn,  and  the  process 
is  called  burning  or  combustion. 

Combustible  substances  burn  with  much  greater 
vigor  in  pure  oxygen  than  in  air.  The  reason  for 
this  is  that  the  air  contains  about  four  times  as 
much  (by  volume)  of  other  gases,  nitrogen,  argon, 
etc.,  as  it  does  of  oxygen.  Part  of  the  heat  of  com- 
bustion is  expended  in  raising  the  temperature  of 
these  gases,  and,  as  the  emission  of  light  is  greater 


Oxygen  and  Ozone  29 

the  higher  the  temperature,  combustions  in  oxygen 
are  much  brighter  than  in  air.  When  substances 
combine  with  oxygen  without  much,  if  any,  mani- 
festation of  light  and  with  but  little  change  of  tem- 
perature, the  process  is  known  as  slow  combustion. 

32.  Nomenclature.     When   oxygen   combines 
with  a  single  other  element,  the  compound  is  called 
an  oxid ;  thus,  mercuric  oxid,  a  compound  of  mercury 
and  oxygen.    The  prefixes  di  and  bi  and/^r  serve  to 
distinguish  the  different  oxids  of  the  same  element. 
Thus,  manganese  dioxid  and  sodium  peroxid  contain 
more  oxygen  than  do  manganese  oxid  arid  sodium 
oxid. 

33.  Oxidation  and  Reduction.     Any  substance 
containing  oxygen  which  under  suitable  conditions 
can  be  transferred  to  another  substance  is  called 
an  oxidizing  agent.     The  oxidizing  agent  is  thereby 
more  or  less  deprived  of  its  oxygen  and  is  said  to 
be  reduced.     A  reducing  agent  then  is  a  substance 
that  takes  the   oxygen   from  an  oxidizing  agent. 
Oxidation  is  the  addition  of  oxygen ;    reduction  is 
the  subtraction  of  oxygen.      When  one  substance 
is  oxidized,  another  is  always  reduced. 

DEFLAGRATION.  As  union  between  a  combustible 
substance  and  an  oxidizing  agent  can  take  place  only 
where  the  two  come  in  contact,  the  rapidity  of  com- 
bustion is  increased  by  making  the  surface  between  the 
combustible  and  oxidizing  agent  greater.  This  can  be 
accomplished  by  grinding  them  into  powders  and  mix- 
ing- them  thoroughly.  Oxidation  may  then  be  effected 
with  great  rapidity  throughout  the  whole  mixture.  To 
such  a  sudden  union  of  combustible  and  oxidizer  is 
given  the  name  of  deflagration.  * 

Gunpowder  is  a  familiar  example  of  such  a  defla- 
grating mixture  ;  the  oxidizing  agent  is  saltpeter  and 


3O  Elementary  Chemistry 

the  reducing  agents  charcoal  and  sulfur.  As  the 
oxids  of  carbon  and  sulfur  are  gaseous,  a  large  volume 
of  gas  is  formed  by  the  ignition  of  the  powder,  and 
if  the  powder  be  confined  in  the  barrel  of  a  gun,  this 
sudden  and  enormous  increase  of  volume  calls  forth  a 
corresponding  pressure ;  the  result  is  that  the  bullet  is 
shot  out  of  the  gun. 

34.  Uses.     In  a  state  of  purity  oxygen  is  used 
in   producing  the  calcium  light   (§44)  and  in   the 
treatment  of  lung  diseases.     As  it  occurs  in  the  air 
it  combines  with  combustibles,  as  coal,  wood,  etc., 
to  furnish  us  with  light,  heat,  and  power.     It  is 
also  indispensable  in  respiration,  fermentation,  and 
most  kinds  of  decay. 

OZONE 

HISTORICAL  NOTE.  Van  Marum  in  1785  observed 
that  during  the  working  of  a  static  electrical  machine 
a  peculiar  odor  was  noticeable,  and  that  mercury  in.  the 
vicinity  of  the  machine  was  tarnished.  This  "  electrical 
smell"  was  investigated  in  1840  by  Schonbein,  who 
proved  that  it  was  due  to  the  presence  of  a  new  form 
of  oxygen. 

35.  Allotropy.      Ozone  is  but  another  form  of 
oxygen.     This  is  proved  by  the  following  facts  : 

/.  Ozone  can  be  completely  transformed  into 
ordinary  oxygen. 

2.  A  given  weight  of  ozone  yields  an  equal 
weight  of  ordinary  oxygen. 

j.  Two  volumes  of  ozone  give  three  volumes  of 
ordinary  oxygen. 

4.  Three  volumes  of  ordinary  oxygen  yield  two 
of  ozone. 

There  are  then  two  varieties  of  the  element  oxy- 
gen. These  are  called  allotropic  forms  or  allotropes 


Oxygen  and  Ozone  31 

of  the  element.  A  few  other  elements  also  may  be 
obtained  in  allotropic  modifications  which  often 
exhibit  quite  different  chemical  properties. 

36.  Occurrence.  Ozone  is  found  in  the  air  in 
very  small  proportions,  chiefly  during  and  directly 
after  thunder  storms.  It  is  formed  by  the  action 
of  the  lightning  on  the  oxygen  in  the  air. 


Fig.  4 A    SIMPLE    FORM    OF  OZONIZER 

Ozonizers  (Fig.  4)  consist  of  two  electrical  conductors  between 
which  oxygen  may  be  passed.  The  conductors  are  connected 
with  an  induction  coil,  and  when  the  current  is  passed  a  multitude 
of  tiny  sparks  strike  through  the  oxygen,  .converting  it  in  part 
into  ozone.  In  the  apparatus  in  the  figure  one  conductor  is  a 
straight  copper  wire  running  through  the  tube,  and  the  other  is  a 
wire  coiled  around  the  tube.  To  the  right  is  an  oxygen  generator 
(by  action  of  water  on  sodium  peroxid).  The  left  end  of  the  tube 
is  left  bare  and  a  roll  of  wire  gauze  slipped  over  it  to  spread  the 
heat  of  a  Bunsen  flame  used  to  decompose  the  ozone  as  it  passes 
out  of  the  tube. 

37.  Preparation.  In  most  chemical  reactions 
proceeding  at  low  temperature  and  producing 
oxygen,  ozone  is  also  formed  in  small  proportion. 


32  Elementary  Clicmistry 

If  a  stick  of  phosphorus  be  scraped  clean  and  put 
into  a  bottle  containing  enough  water  to  nearly 
cover  it,  ozone  will  soon  be  formed  in  the  bottle. 
Also,  if  a  red-hot  glass  rod  be  plunged  into  a  flask 
filled  with  a  mixture  of  air  and  ether  vapor,  ozone 
is  produced.  The  best  way  to  prepare  ozone, 
however,  is  by  the  action  of  electrical  discharges 
on  oxygen  in  an  apparatus  called  an  "ozonizer." 

38.  Properties.  Physical.  Ozone  is  a  colorless 
gas  with  a  peculiar  and  irritating  odor.  When 
liquefied  it  is  of  an  intensely  blue  color.  It  is 
quite  soluble  in  turpentine,  while  oxygen  is  very 
slightly  so.  Hence  ozone  may  be  separated  from 
oxygen  by  solution  in  that  solvent. 

CJicmicaL  Ozone  is  totally  decomposed  into 
oxygen  at  temperatures  above  20°.  It  is  a  most 
energetic  oxidizing  agent.  It  decomposes  potas- 
sium iodid  in  solution,  setting  the  iodin  free,  which, 
if  brought  in  contact  with  starch,  forms  a  blue 
compound. 

Problems 

/.  Potassium  chlorate  when  heated  decomposes  into  oxygen 
and  potassium  chlorid.  What  is  the  per  cent  of  potassium  chlorid 
in  the  chlorate  if  22 <?"•  of  the  chlorate  yield  8.62<?"-  of  oxygen  ? 

2.  If  potassium  chlorate  contains  39.2  per  cent  of  oxygen, 
how  many  grams  of  oxygen  can  be  obtained  from  20^-  of  potas- 
sium chlorate? 

j.  How  many  liters  of  oxygen  under  standard  conditions  can 
be  obtained  from  lotf-  of  potassium  chlorate? 

4.  How  many  liters  of  oxygen  at  50°  and  700 '«>«•  pressure  can 
be  obtained  from  log-  of  potassium  chlorate,  containing  10  per 
cent  of  potassium  chlorid  ? 

5.  How  much  oxygen  was  given  off  from  how  much  potas- 
sium chlorate,  if  the  residue  of  potassium  chlorid  amounted  to 
3.4^-? 


CHAPTER  IV 

HYDROGEN 

HISTORICAL  NOTE.  That  acid  liquors,  when  brought 
in  contact  with  iron  or  zinc,  effervesce  and  give  off  a 
"wind, "was  known  at  quite  an  early  period,  but  the 
gas  thus  generated  was  supposed  not  to  differ  from 
atmospheric  air.  Cavendish, 'an  Englishman,  isolated 
the  gas  in  1776  and  studied  its  properties,  and  Lavoisier 
gave  it  the  name  of  hydrogen,  i.  e.,  water  producer, 
because  the  sole  product  of  its  combustion  is  water. 

39.  Occurrence.    Hydrogen  occurs  free  in  small 
proportions  in  the  extreme  upper  regions  of  the 
atmosphere    of   the    earth,  and    in    some   volcano 
gases,  but  is  present  in  enormous  quantities  in  the 
sun's  atmosphere.     It  forms  11.19  Per  cent  of  the 
weight  of  water  and  is  a  constituent  of  most  animal 
and  vegetable  substances. 

40.  Preparation.    A  current  of  electricity  passed 
through  water  decomposes   it  into  hydrogen   and 
oxygen.     At  high  temperatures  water  dissociates 
(page  60)  into  oxygen  and  hydrogen,  and  if  some 
substance,  as  iron,  is  present,  this  will  unite  with 
the  oxygen  to  form  a  solid  compound,  the  hydrogen 
going  free.     By  passing  steam  over  very  hot  iron, 
then,  hydrogen  may  be  prepared.    The  alkali  metals 
(page  183)  and  the  alkalin  earth  metals  (page  251) 
react  with  water,  setting  half  of  its  hydrogen  free 
and   forming    'hydro* ids  of   the   respective   metals, 
which  dissolve  in  the  excess  of  water  present.    The 
hydrogen  of  these  hydroxids  can  be  expelled  by 

[33] 


34 


Elementary  Clicmistry 


the  action  of  aluminum 
or  zinc  on  their  solu- 
tions, or  by  heating  the 
solid  hydroxids  with 
powdered  iron  or  zinc. 
Acids  when  acted  upon 
by  certain  metals,  espe- 
cially magnesium,  zinc, 
and  iron,  yield  hydro- 
gen. Zinc  and  dilute 
sulf uric  or  hydrochloric 
acids  are  usually  used. 

Kipp's  gas  generator  (Fig. 
5)  is  a  convenient  apparatus 
for  supplying  hydrogen  at  any 
time.  The  solid  (zinc)  is  placed 
in  the  middle  globe  and  the 
liquid  (dilute  sulfuric  acid) 
in  the  upper.  By  opening  the 
stopcock  between  the  upper 
and  the  middle  globes,  the 
acid  flows  down  upon  the  zinc, 
and  the  gas  generated  escapes 
through  the  stopcock  delivery 
tube  at  the  right.  If  this  stop- 
cock is  closed,  the  gas,  hav- 
ing no  outlet,  comes  under  a 
greater  and  greater  pressure, 
and  the  liquid  which  has  run 
through  the  solid  into  the  lowest  compartment  is  finally  forced  up 
through  the  rubber  tube  at  the  left,  into  the  upper  globe,  the 
excess  of  the  gas  escaping  through  the  funnel  tube. 

41.  Physical  Properties.  (Table  I.,  Appendix 
D.)  Hydrogen  is  a  colorless,  odorless,  and  tasteless 
gas,  but  slightly  soluble  in  water  and  other  liquids ; 
it  is  the  lightest  known  substance. 


Fig.   5 KIPP'S  GAS  GENERATOR 


Hydrogen  35 

DIFFUSION  ;  TRANSPIRATION.  Hydrogen  is  charac- 
terized by  the  rapidity  with  which  it  mixes  with  other 
gases  (diffusion]  and  the  ease  with  which  it  passes 
through  porous  plates  of  plaster  of  paris,  plumbago, 
etc.,  and  narrow  tubes  (transpiration),  Graham,  who 
made  a  study  of  the  transpiration  of  gases,  discovered 
the  following  law : 

The  zv  eights  of  gases  taking  equal  times  to  pass 
through  the  same  porous  plate  under  similar  conditions 
are  inversely  proportional  to  the  square  roots  of  their 
specific  gravities. 

Thus,  the  specific  gravity  of  oxygen  referred  to 
hydrogen  is  16;  hence  hydrogen  traverses  porous  plates 
four  times  as  fast  as  does  oxygen. 

42.  Chemical  Properties.     Hydrogen  burns  in 
the  air  with  an  extremely  hot  and  almost  invisible 
flame ;   in  oxygen   its   combustion   is  much  more 
vigorous.     Under  certain  conditions  it  can  unite 
with   oxygen   already  in  combination  with   other 
elements.     Thus,  when  lead  or  copper  is  heated  in 
contact  with  oxygen,  oxids  of  lead  or  copper  are 
formed.      If  these  oxids  are  heated  in  an  atmos- 
phere of  hydrogen,  the  oxygen  leaves  the  metals 
and    unites   with    the    hydrogen,   forming  water. 
Hydrogen  may  thus  act  as  a  reducing  agent  (§  33). 

LIQUID  HYDROGEN.  Liquid  hydrogen  is  colorless, 
has  a  clearly  defined  surface,  drops  well,  and  can  be 
poured  from  one  vessel  to  another.  It  is  a  non-conductor 
of  electricity  and  is  very  slightly  magnetic.  It  is  the 
lightest  known  liquid,  being  only  one-fourteenth  as 
heavy  as  water.  It  is  the  coldest  liquid  known,  boiling 
under  ordinary  pressure  at  20.5°  absolute,  and  it  may 
be  solidified  into  a  clear,  transparent  ice. 

43.  Nascent  State.     While  hydrogen  does  not 
react  with  most  other  elements  except  at  tempera- 
tures somewhat  above  500°,  yet,  at  the  moment  of 
its  formation,  when  it  is  said  to  be  in  the  nascent 


36  Elementary  Chemistry 

state,  it  brings  about  reactions  even  at  ordinary 
temperatures.  Similarly,  oxygen,  the  moment  it  is 
set  free  from  combination  acts  more  powerfully 
than  afterward.  The  great  oxidizing  power  of  ozone 
is  perhaps  due  to  nascent  oxygen,  ozone  breaking 
up  into  oxygen. 

44.  Uses.  Hydrogen  is  used  to  inflate  balloons, 
but  is  especially  employed  in  attaining  high  tem- 
peratures by  its  combustion  in  oxygen,  whereby  a 

temperature  of 
nearly  2,800°  may 
be  reached.  In 
the  production  of 

Fig.  6 — SECTIONAL    VIEW    OF    AN    OXYHYDROGEN          tlllS  nign  temper- 

ature,  great  care 

must  be  taken  to  prevent  the  mixing  of  the  gases 
before  they  are  burned,  else  most  serious  explo- 
sions may  result.  A  burner  of  the  form  shown  in 
Fig.  6  may  be  safely  used.  This  consists  of  an  outer 
tube,  drawn  down  to  a  tip  at  one  extremity  and 
furnished  with  a  stopcock  at  the  other.  In  the  axis 
of  this  tube  is  a  second  similar  tube,  which  can 
be  moved  to  and  fro.  The  hydrogen  is  fed  into  the 
outer  tube  and  the  oxygen  through  the  inner ;  their 
proportions  and  the  relative  positions  of  the  tips 
are  adjusted  until  the  flame  is  thin  and  straight. 
All  danger  of  explosion  is  avoided  by  the  use  of 
such  a  burner,  for  the  gases  do  not  mix  except  at 
the  moment  of  combination.  If  the  oxykydrogen 
flame,  as  that  produced  by  the  burning  of  hydro- 
gen is  called,  is  directed  against  a  piece  of  lime, 
this  is  heated  to  incandescence  and  gives  out  a  very 
brilliant  light  (calcium  light). 


Hydrogen  37 

Exercises 

/.     What  familiar  compounds  contain  hydrogen  ? 

2.  To  what  is  the  danger  of  an  explosion  with  hydrogen  due, 
and  how  may  it  be  avoided  ? 

j.  What  property  of  hydrogen  makes  it  useful  for  inflating 
balloons ?  What  property  makes  it  rather  disadvantageous? 

4.     What  property  of  hydrogen  may  best  serve  as  its  test  ? 

Problems 

/.  The  specific  gravity  of  ozone  is  24,  and  that  of  oxygen  is 
16.  What  is  the  ratio  of  their  speeds  of  transpiration  ? 

2.  The  specific  gravity  of  chlorin  is  nearly  36.  Compare  its 
speed  of  transpiration  with  that  of  hydrogen. 

j.  A  certain  gas  passes  through  a  porous  plate  3.8  times 
slower  than  does  hydrogen.  What  is  its  specific  gravity  ? 

4.  Oxygen  and  hydrogen  are  separated  by  a  porous  partition, 
and  3.84^-  of  hydrogen  pass  through  in  one  second.     What  vol- 
ume of  oxygen  passes  through  in  the  same  time  in  the  opposite 
direction  ? 

5.  One  liter  of  hydrogen  weighs  o.oqg'-  and  one  liter  of  oxygen 
1.43^-    What  is  the  specific  gravity  of  hydrogen  referred  to  oxygen 
as  a  standard  ?    Of  oxygen  referred  to  hydrogen  ? 

6.  What  is  the  volume  in  liters  of  2ff-  of  hydrogen?     Of  32^"- 
of  oxygen  ? 

7.  A  balloon  of  500  cubic  meters  capacity  is  to  be  filled  with 
hydrogen  at  2op  and  800  mm.  pressure.     What  will  be  the  weight 
of  the  hydrogen  ? 

8.  If  hydrogen  chlorid  contains  2.7  per  cent  of  hydrogen,  how 
many  liters  of  hydrogen  at  93°  and  265  mm.  can  be  obtained  from 
38 g.  of  the  chlorid? 

g.  If  water  contains  11.19  Per  cent  of  hydrogen,  how  many 
liters  of  hydrogen  at  16°  and  743  mm.  can  be  obtained  from  one 
kilogram  of  water  ? 

10.  If  23«r-  of  sodium  liberate  one  gram  of  hydrogen  from 
water,  how  many  grams  of  the  metal  must  be  employed  to  prepare 
100  /•  of  the  gas  at  22°  and  752  mm.  ? 

11.  What  is  the  weight  of  a  liter  of  hydrogen  collected  over 
water  at  50°  and  743  mm.  ?    (See  problem  5  for  data.) 

12.  Under  standard  conditions  what  would  be  the  volume  of 
the  gas  considered  in  the  last  problem  ? 


CHAPTER  V 

THE  COMPOUNDS  OF  OXYGEN  AND 
HYDROGEN 

There  are  two  compounds  of  oxygen  and  hydro- 
gen, or  oxids  of  hydrogen  —  hydrogen  monoxid 
(water)  and  hydrogen  dioxid  (peroxid). 

WATER 

HISTORICAL  NOTE.  Water  was  supposed  to  be  an 
element  (page  9)  until  Cavendish  in  1781  showed  that 
it  was  produced  by  the  burning  of  hydrogen. 

45.  Occurrence.  Water  is  found  in  the  atmos- 
phere in  the  form  of  invisible  vapor  which  may 
condense  into  mist,  fog,  or  cloud,  and  these  may  fall 
to  the  earth  as  rain,  hail,  or  snow.  The  rain  or 
melted  snow  and  hail  soak  into  the  ground  and 
collect  in  springs,  rivers,  lakes,  oceans,  etc.  The 
differences  in  these  "  natural  waters"  are  due  to  the 
dissolved  substances  they  contain.  Nearly  all  vege- 
table and  animal  substances  contain  more  or  less 
water  which  escapes  when  they  are  heated  or  other- 
wise dried. 

THE  "  NATURAL  WATERS."  Rain  water  is  nearly 
pure  water,  containing  only  the  impurities  which  were 
present  in  the  air  through  which  it  fell.  The  common- 
est of  these  impurities  are  ammonia,  nitric  acid,  and 
saline,  vegetable  and  animal  substances. 

Spring  water  is  rain  water  which  has  soaked  into 
the  ground.  The  water  descends  until  it  comes  to  an 
impervious  stratum,  along  which  it  flows  to  collect  in 
some  hollow,  or  to  issue  at  the  surface  of  the  earth,  often 

[38] 


The  Compounds  of  Oxygen  and  Hydrogen        39 

many  miles  from  where  it  entered.  Spring  waters  hold 
in  solution  various  substances,  depending  upon  the 
nature  of  the  ground  over  which  they  pass.  Mineral 
waters  are  spring  waters  containing  certain  substances 
of  peculiar  taste,  many  of  which  are  reputed  to  be  of 
medicinal  value.  They  may  be  classed  into  :  Saline 
waters,  containing  common  salt ;  alkalin  ivaters,  con- 
taining common  soda ;  bitter  ivaters,  containing  mag- 
nesium compounds  ;  chalybeate  waters,  containing  iron 
compounds  ;  aerated  waters,  containing  carbonic  acid 
gas ;  sulfur  waters,  containing  hydrogen  sulfid. 

River  water  is  derived  from  rain  and  spring  water. 
The  substances  held  in  suspension  or  solution  by  it 
depend  upon  the  nature  of  the  river  bed  as  well  as  of 
the  waters  flowing  into  it. 

Sea  water  is  chiefly  concentrated  river  water.  The 
dissolved  substances  contained  in  the  waters  of  the 
rivers  discharging  into  the  sea  or  ocean  are  mostly  non- 
volatile, and  hence  are  left  behind  when  the  sea  water 
evaporates.  The  vapor  is  very  often  carried  far  inland, 
only  to  be  precipitated  to  flow  back  again  into  the  sea. 
This  perpetual  washing  out  or  leaching  of  the  soil 
results  in  a  continually  increasing  proportion  of  soluble 
matter  in  the  sea,  and  it  may  be  truly  said  that  the  sea 
contains,  in  minute  traces,  at  least,  every  soluble  sub- 
stance on  the  earth.  Common  salt  is  the  main  dissolved 
substance  in  sea  water.  The  water  of  inland  bodies  of 
water  without  any  outlet,  as  the  Great  Salt  Lake  in 
Utah,  is  also  salty. 

46.  Distillation.  The  process  known  as  distil- 
lation consists  in  converting  a  liquid  into  vapor, 
separating  the  vapor  from  the  liquid,  and  then  con- 
densing it.  The  apparatus  consists  of  a  part  to 
vaporize  the  liquid,  usually  called  a  still,  and  a  part 
to  condense  the  vapor,  sometimes  called  a  ivorm  and 
sometimes  a  condenser.  The  liquid  is  boiled  in  the 
still  5  (Fig.  7),  its  vapor  passing  into  the  coiled, 
wormlike  tube  W,  around  which  cold  water  is  made 
to  circulate. 


40  Elementary  Chemistry 

A  form  in  common  use  in  laboratories  (Fig.  8) 
consists  of  a  flask  connected  by  means  of  a  curved 
tube  and  corks,  with  a  condensing  apparatus  called 
a  Liebigs  condenser.  This  is  simply  a  straight  tube 
running  through  the  axis  of  a  larger  but  shorter 
tube  through  which  a  current  of  cold  water  is  made 
to  pass. 

Substances  which  are  practically  involatile  at 
ordinary  temperatures  may  be  separated  from  the 
liquids  with  which  they  are  mixed  by  distillation. 
The  separation  of  a  mixture  of  volatile  substances, 
as  water  and  alcohol,  by  means  of  distillation,  is  but 
partial,  the  distillate  always  containing  some  of  all 
the  substances,  the  more  volatile  in  the  greater 
proportion. 


Fig.   7 STILL  AND  CONDENSER 

47.  Filtration.  The  process  of  passing  a  liquid 
impregnated  with  or  holding  in  suspension  solid 
particles,  through  some  porous  material,  as  paper, 
cloth,  sand,  charcoal,  etc.,  is  known  as  nitration. 
If  the  pores  be  small  enough,  all  the  solid  matter 
may  be  removed.  It  is  hard,  however,  to  prepare 


The  Compounds  of  Oxygen  and  Hydrogen        41 

filters  with  fine  enough  pores  to  remove  bacteria, 
etc.,  from  water,  although  some  kinds  of  baked  clay 
succeed  fairly  well. 


Fig.  8 — APPARATUS  FOR  DISTILLING  SMALL  QUANTITIES  OF  LIQUID 

FILTRATE  AND  PRECIPITATE.  The  liquid  which  passes 
through  is  called  &  filtrate.  When  on  mixing  one  liquid 
with  another,  an  insoluble  solid  is  formed,  this  is  said 
to  be  precipitated  and  is  known  as  a  precipitate. 

PURIFICATION  OF  DRINKING  WATER  BY  FILTRATION. 
Wholesome  drinking  or  potable  water  should  be  clear, 
free  from  disease  germs,  and  should  not  contain  too 
much  mineral  matter  in  solution,  although  a  little  does 
no  harm.  A  source  of  pure  water  is  not  available  in 
some  cities;  hence  recourse  must  be  had  to  purifying 
processes.  Boiling  the  water  kills  the  germs,  but  is  too 
expensive  for  use  on  a  large  scale.  Coagulation  filters 
and  intermittent  sand  filters,  Or  the  two  combined,  have 
proved  successful  in  many  cases.  Fine  particles  of  clay, 
etc.,  may  remain  suspended  in  water  for  a  long  time, 
but  if  minute  proportions  of  certain  substances,  as 
alum,  etc.,  be  added,  the  particles  flock  together  and 
settle  much  more  rapidly.  A  considerable  proportion 
of  the  disease  germs  clings  to  these  particles  and  is 


42  Elementary  Chemistry 

thus  separated  from  the  water.  Subsequent  filtration 
through  coke  dust  and  sand  removes  the  coagulated 
particles,  together  with  the  germs  adhering  to  them. 

In  the  intermittent  process,  beds  of  sand  several 
acres  in  extent  are  prepared,  the  upper  layers  consisting 
of  fine,  the  lower  of  coarse  sand.  Tile  drains  are  set  in 
the  lower  layers  to  collect  and  conduct  to  a  reservoir 
the  purified  water  that  filters  through.  These  beds  are 
flooded  with  water  which  is  treated  with  some  coagu- 
lating agent.  After  the  water  soaks  through,  the  sand 
is  allowed  to  dry  and  flooding  is  repeated. 

The  taste  and  wholesomeness  of  water  also  depend 
to  some  extent  upon  the  dissolved  gases  it  contains. 
Water  deprived  of  its  dissolved  gases  by  boiling  tastes 
flat;  its  taste  may  be  improved  by  shaking  it  up  with  air. 

48.  Formation.      Water  is  formed  in  all  the 
phenomena  of  nature  in  which  hydrogen  is  oxi- 
dized.    As  wood  and  similar  combustibles  contain 
hydrogen,    water    is    produced    when    they    burn. 
Also,  as  hydrogen  is  a  constituent  of  most  animal 
and  vegetable  substances,  water  is  formed  when 
they  putrefy  and  decay. 

49.  Preparation.     The  combustion  of  hydrogen 
or  of  substances  containing-  hydrogen  yields  water. 
Hydrogen    starts  to   burn   only    when    heated   to 
temperatures  above   600°.      At   ordinary   tempera- 
tures, mixtures  of  hydrogen  and  oxygen  may  be 
preserved    indefinitely    without    any    appreciable 
combination  occurring.     The  same  is  true  of  the 
chemical  union  of  many  other  substances. 

As  a  rule,  low  temperatures  tend  to  prevent 
reaction,  while  high  temperatures  aid  it.  If  one 
portion  of  a  mixture  of  hydrogen  and  oxygen  be 
heated  to  the  combining  temperature,  union  ensues 
with  evolution  of  enough  heat  to  bring  the  neigh- 
boring portions  up  to  the  combining  temperature 


The  Compounds  of  Oxygen  and  Hydrogen        43 


so  that  they  unite  also.  Union  of  the  whole  mix- 
ture is  thus  rapidly  effected,  and  the  sp'eed  with 
which  the  union  spreads  through  the  mixture  has 
been  found  to  be  2,810  meters  per  second. 

50.  The  Volumetric  Composition  of  Water  by 
Eudiometric  Measurements.  The  instrument  gen- 
erally employed 
to  show  the 
union  of  meas- 
ured volumes  of 
gases  is  the  eudi- 
ometer. One  of 
the  simplest 
forms  consists  of 
a  straight  tube 
60  to  80 cm-  long, 
in  the  closed  end 
of  which  are 
sealed  two  plati- 
num wires  with 
their  inner  ex- 
tremities quite 
close  together. 
The  eudiometer 
is  filled  with 
mercury  and  in-  pig.  9— 
verted  in  a  mer- 
cury pneumatic 
trough.  (Fig.  9.) 
Some  dry  hydrogen  is  made  to  pass  up  the  tube  to 
expel  some  of  the  mercury.  The  volume  of  the  gas 
added  is  read  and  reduced  to  standard  conditions 
of  temperature  and  pressure  (§  27).  A  volume  of 


EUDIOMETER   AND   MERCURY   PNEUMATIC 
TROUGH 

The  sides  of  the  trough  are  of  plate  glass  so  that  ths 
level   of   the  mercury  may  be   accurately  seen.     The 
slanting  support   at    the  left  is  used  to  lay  the  eudi- 
ometer on  when  a  gas  is  introduced 


44 


Elementary  Chemistry 


dry  oxygen  a  little  larger 
than  that  of  the  hydrogen  is 
then  introduced,  measured 
and  reduced  to  standard 
conditions.  (Fig.  10.) 

To  start  the  reaction,  the 
outer  extremities  of  the 
platinum  wires  are  con- 
nected to  the  terminals  of 
an  induction  coil  and  the 
circuit  closed.  The  electric 
sparks  between  the  wires 
heat  the  mixture  in  their 
vicinity  to  the  combining 
temperature,  and  all  the 
hydrogen  burns  with  almost 
explosive  violence.  The 
volume  of  the  water  pro- 
duced is  so  small  in  com- 
parison with  the  volumes  of 
the  gases  that  it  may  with- 
out appreciable  error  be 
•^  neglected.  The  volume  of 

the  residual  oxygen  is 
measured,  reduced  to  stand- 
ard conditions,  and  sub- 
tracted from  the  volume  of 
oxygen  taken  at  first.  This 
difference  is  the  volume  of 
oxygen  combining  with  the 
volume  of  hydrogen  taken.  The  ratio  of  these  vol- 
umes is  found  to  be  i  :  2.  One  volume  of  oxygen 
combines  with  two  volumes  of  hydrogen.  If  the 


Fig.  10 ANOTHER  FORM  OP 

EUDIOMETER 

By  bending  it  around  so  as  to  form 

a  U  tube,  the  second  branch  acts  as 

a  pneumatic  trough 


The  Compounds  of  Oxygen  and  Hydrogen        45 

experiment  be  conducted  at  temperatures  above 
1 00°,  so  that  the  water  formed  vaporizes,  and  the 
volume  of  the  steam  be  measured,  its  reduced  vol- 
ume will  be  found  to  equal  that  of  the  hydrogen. 

Two  volumes  of  hydrogen  unite  with  one  volume  of 
oxygen  to  give  two  volumes  of  water  vapor. 

51.  Volumetric  Laws  of  Chemical  Combination. 
The  experiment  just  described  has  been  repeated 
many  times,  always  with  the  same  result.  Two 
facts  taught  by  it  are  of  fundamental  importance : 

/.  The  same  volume  of  water  vapor  always 
results  from  the  union  of  the  same  volumes  of 
oxygen  and  hydrogen.  There  is  a  fixity,  a  definite- 
ness  in  the  proportions  of  the  volumes.  This 
definiteness  has  been  found  in  the  combination  of 
all  gases,  although  the  proportion  may  vary  from 
case  to  case.  These  facts  are  summed  up  in  the 
Law  of  Definite  Proportions  by  Volume : 

The  same  volumes  of  reacting  gases  always  produce 
the  same  volumes  of  gaseous  compounds. 

2.  Two  volumes  of  water  vapor  are  produced 
by  the  union  of  two  volumes  of  hydrogen  and  one 
volume  of  oxygen  ;  the  volumes  of  the  gases  are  in 
the  ratio  2:2:1.  What  is  striking  in  this  fact  is 
that  the  ratio  is  expressible  by  small,  whole  numbers. 
It  is  certainly  remarkable  that  of  all  conceivable 
ratios  such  simple,  integral  ones  should  be  found. 
Other  gases  behave  similarly,  although  the  ratios 
may  be  different,  and  the  facts  find  their  general 
expression  in  the  Law  of  Volumetric  Proportions: 

77?^  volumes  of  reacting  gases  stand  in  a  simple, 
integral  ratio  to  one  another  and  to  the  volumes  of  the 
gases  produced. 


46  Elementary  Chemistry 

52.  Law  of  Definite  Proportions  by  Mass  or 
Weight.  One  liter  each  of  hydrogen,  oxygen,  and 
water  vapor  weighs  0.09 *"-,  1.43*"-,  and  0.805^-,  respec- 
tively. The  ratio  of  these  numbers  is  nearly  1:16:9. 
(To  avoid  overtaxing  the  memory  with  decimals, 
these  numbers  are  rounded  off  to  the  nearest  inte- 
gers.) Now,  2  L  of  hydrogen  combine  with  i  L  of 
oxygen  to  give  2  L  of  water  vapor.  Hence,  2  x  0.09 
(=  o.i 8)^-  of  hydrogen  unite  with  1.43^-  of  oxygen 
to  give  2  X  0.805  ( =  i  .6 1  )*"•  of  water  vapor,  or,  round- 
ing off  to  the  nearest  integers,  one  part  of  hydro- 
gen combines  with  eight  parts  of  oxygen  to  produce 
nine  parts  of  water. 

We  may  arrive  at  the  same  conclusion  by  a 
slightly  different  way.  The  specific  gravities  (re- 
ferred to  hydrogen)  of  water  vapor  and  of  oxygen 
are  9  and  16,  respectively.  Then  two  volumes  of 
water  vapor  and  one  volume  of  oxygen  weigh, 
respectively,  9  and  8  times  as  much  as  two  volumes 
of  hydrogen.  Hence,  as  these  are  the  volumes 
required  in  the  reaction  of  hydrogen  and  oxygen 
to  produce  water,  nine  parts  of  water  are  produced 
by  the  union  of  eight  parts  of  oxygen  with  one  part 
of  hydrogen. 

Innumerable  experiments  have  shown  that  this 
is  always  true  of  water :  the  ratios  of  combination 
by  mass  or  weight  are  fixed  and  invariable.  Simi- 
lar conclusions  have  been  arrived  at  for  every  other 
definite  compound.  All  such  facts  find  their  gen- 
eral expression  in  the  Law  of  Definite  Proportions 
by  Mass  or  Weight : 

A  definite  compound  always  contains  the  same  constit- 
uents united  in  the  same  proportions  by  mass  or  weight. 


The  Compounds  of  Oxygen  and  Hydrogen        47 

53.  Composition  of  Water  by  Gravimetric  Meas- 
urements. The  proportions  in  which  oxygen  and 
hydrogen  tmite  to  form  water  can  also  be  ascer- 
tained by  operations  involving  determinations  of 
weight  alone.  When  copper  is  heated  in  the  air, 
it  combines  with  oxygen  and  forms  the  black  oxid 
of  copper.  This  when  heated  in  hydrogen  loses 


Fig.    II APPARATUS  FOR   SHOWING  THE  COMPOSITION  OF  WATER 

GRAVIMETRICALLY 

its  oxygen  which  unites  with  hydrogen  to  form 
water,  and  the  copper  oxid  is  thus  reduced  (§42). 
The  water  can  be  collected  by  passing  its  vapor 
over  some  substance,  as  calcium  chlorid,  which 
will  absorb  it.  The  apparatus  (Fig.  u)  consists  of 
a  hydrogen  generator,  a  wash  bottle,  A,  partially 
filled  with  potassium  permanganate  solution,  a 
wash  cylinder^  B,  containing  some  strong  sulfuric 
acid,  a  U-tube,  C,  filled  with  calcium  chlorid,  a 
hard  glass  tube,  D,  about  20  cm-  long  and  i  cm-  in 
bore,  and  a  second  chlorid  of  calcium  tube,  E, 


48  Elementary  Chemistry 

serving  to  retain  the  water  formed.  The  potassium 
permanganate  solution  removes  certain  impurities 
from  the  hydrogen,  while  the  sulfuric  acid  and  cal- 
cium chlorid  dry  it. 

The  hard  glass  tube  is  thoroughly  dried,  the 
middle  part  nearly  filled  with  dry  copper  oxid  and 
carefully  weighed.  The  second  chlorid  of  calcium 
tube,  E,  is  also  weighed.  The  apparatus  is  then  put 
together  as  shown,  and  hydrogen  passed  through  it. 
As  soon  as  the  hydrogen  has  driven  out  all  of  the 
air,  the  portion  of  the  tube  underneath  the  oxid  is 
heated  nearly  to  redness.  When  the  black  color  of 
the  oxid  has  changed  to  red,  the  reduction  is  com- 
plete. The  heating  is  then  discontinued  and  the 
current  of  hydrogen  kept  passing  until  the  tube  is 
cool.  The  tube  and  copper,  and  the  chlorid  of  cal- 
cium tube  are  again  weighed.  The  loss  of  weight  of 
the  former  is  equal  to  the  weight  of  the  oxygen  given 
up  by  the  copper  oxid,  and  the  increase  in  the  weight 
of  the  latter  is  the  weight  of  the  water  formed. 

The  difference  between  the  weights  of  the  water 
and  of  the  oxygen  is  the  weight  of  the  hydrogen 
used.  The  weights  of  the  hydrogen  and  oxygen 
required  to  produce  the  weight  of  water  formed 
have  thus  been  found.  For  example,  Berzelius  and 
Dulong,  who  in  1820  originated  this  experiment, 
found  the  loss  in  weight  of  the  tube  containing  the 
copper  oxid  to  be  27.129  <£"•,  and  the  gain  in  weight 
of  the  chlorid  of  calcium  tube  to  be  30.519^-,  i.  e., 
30.519^-  of  water  were  formed  containing  27.129^-  of 
oxygen.  Hence,  3.390  *"•  (the  difference  between 
30.519  and  27.129)  of  hydrogen  must  have  combined 
with  27.129^.  of  oxygen  to  produce  30.51 9  ^  of  water. 


The  Compounds  of  Oxygen  and  Hydrogen        49 

The  ratio  of  these  numbers — 3.390  :  27.129  :  30.519 
—  is  approximately  the  same  as  i  18:9  or  11.19: 
88.8 1  :  100. 

54.  Relations  Between  the  Laws  of  Definite 
Proportions.  Water  then  consists  of  88. 8 1  per  cent 
of  oxygen  and  11.19  Per  cent  °f  hydrogen.  Now 
as  0.805  £'•  of  water  vapor,  0.09  *"•  of  hydrogen,  and 
1.43^-  of  oxygen,  each  occupy  the  space  of  one 
liter,  100  *"•  of  water  vapor  occupy  100/0.805  =  124  L 
(rounding  off  to  the  nearest  integer),  88. 8 1  #.  of  oxy- 
gen occupy  88.81/1.43  =  62  L,  and  1 1.19^-  of  hydrogen 
occupy  1 1.19/0.09  =  124  L.  The  ratio  of  these  num- 
bers—  124  :  62  :  124  —  is  the  same  as  2  :  i  :  2,  just  as 
has  already  been  directly  found.  In  Berzelius  and 
Dulong's  determination,  the  3.390^-  of  hydrogen 
occupied  3.390/0.09  =  38  7-,  the  27.129^-  of  oxygen, 
27.129/1.43=  19  7-,  the  30.519^  of  water  vapor, 
30.5 1 9/0.805  =  38 7-,  and  these  volumes  are  again  seen 
to  be  in  the  ratio  of  2  :  i  :  2. 

Knowing  then  the  percentage  composition  of 
water  and  the  weights  of  equal  volumes  of  hydro- 
gen, oxygen,  and  water  vapor,  we  can  compute  the 
volumes  of  the  gases  entering  into  and  produced 
by  the  reaction  yielding  water.  From  the  Law  of 
Definite  Proportions  by  Mass  we  can  pass  to  that 
of  Definite  Proportions  by  Volume.  We  have 
already  (§  52)  learned  how  to  pass  from  the  Law  of 
Definite  Proportions  by  Volume  to  that  of  Definite 
Proportions  by  Mass.  The  laws  are  thus  seen  to  be 
identical  in  essence.  Attention  has  already  (§  14) 
been  directed  to  the  invariable  composition  which 
is  one  of  the  items  that  distinguishes  a  mixture 
from  a  compound. 


Elementary  Chemistry 


55.  Law  of  Conservation  of  Matter  ( Persist- 
ence of  Mass).  Eight  parts  of  oxygen  combine 
with  one  part  of  hydrogen  to  produce  nine  parts 
of  water ;  the  sum  of  the  weights  of  the  hydrogen 
and  oxygen  is  equal  to  the  weight  of  the  water. 

Like  results  have  been 
found  to  be  true  of  all 
reactions : 

The  sum  of  the  masses  of 
the  reacting  substances  or  fac- 
tors is  equal  to  the  sum  of  the 
masses  of  the  substances  pro- 
duced or  products. 

But  this  is  the  Law  of 
Conservation  of  Matter 

(§•5). 

56.  Synthesis  and 
Analysis.  By  burning  hy- 
drogen in  oxygen  we  have 
effected  the  synthesis  of 
water,  i.e.,  we  have  put 
hydrogen  and  oxygen  to- 
gether in  proper  propor- 
tions and  under  suitable 
conditions  and  have  ob- 
tained water.  Its  synthesis 
was  also  effected  by  bring- 
ing hydrogen  into  contact  with  hot  copper  oxid, 
which  itself  was  decomposed  into  copper  and  oxy- 
gen. In  the  first  case,  account  was  taken  of  the 
volumes ;  in  the  second,  of  the  weights.  The  oppo- 
site of  synthesis  is  analysis,  and  we  now  proceed  to 
ascertain  the  composition  of  water  analytically. 


Fig.    12 VOLTAMETER 

Lecture-table  form 


The  Compounds  of  Oxygen  and  Hydrogen        51 

57.  Analysis  of  Water.  Water  may  be  decom- 
posed into  its  elements  by  passing  a  current  of 
electricity  through  it.  As  water  itself  is  a  very  poor 
conductor  of  electricity,  a  small  proportion  of  an 
acid  or  alkali  is  added  to  increase  its  conductance. 
The  instruments  employed  are  called  voltameters, 
and  consist  essentially  of  two  electrodes  or  places  for 
the  entrance  and  exit  of  the  electric  current,  and 
two  graduated  tubes  to  collect  the  gas  rising  from 
the  electrodes  (Figs.  12  and  13).  The  electrodes 
are  immersed  in  the  liquid, 
the  tubes  filled  with  the 
same  and  inverted  over 
the  electrodes.  As  the  cur- 
rent passes,  gases  arise 
from  the  electrodes  and 
displace  the  liquid  in  the 
tubes.  An  examination  of 
these  gases  shows  that  one 
is  hydrogen  and  the  other  oxygen;  the  volume 
of  the  hydrogen  is  twice  that  of  the  oxygen. 

Water  is  thus  decomposed  into  two  volumes  of 
hydrogen  and  one  of  oxygen.  If  the  liquid  be 
weighed  before  and  after  passing  the  current,  and 
the  weights  of  the  gases  ascertained,  it  will  be 
found  that  the  loss  in  weight  of  the  former  is  equal 
to  the  weights  of  the  latter,  and  that  the  ratio  of 
these  weights  is  9  :  8  :  i.  If  both  the  gases  be 
caught  in  the  same  receiver  (Fig.  14)  and  then  trans- 
ferred to  an  eudiometer  and  exploded,  it  will  be 
found  that  if  the  experiment  be  carried  out  at  tem- 
peratures above  100°,  three  volumes  of  the  mixture 
will  contract  to  two  volumes  of  a  gas  which  proves  to 


Fig.    13 ANOTHER  FORM  OP 

VOLTAMETER 


Elementary  Chemistry 


be  water  vapor.    Now  since  there  were  two  volumes 
of  hydrogen  to  one  of  oxygen,  we  again  see  that 

two  volumes  of 
hydrogen  com- 
bine with  one 
volume  of  oxy- 
gen to  yield  two 
volumes  of  water 
vapor. 

58.  Chemical 
Equations.  The 
Law  of  Definite 
Proportions 
affirms  that  fixed 
relative  amounts 
of  hydrogen  and 
oxygen  react  to 
produce  water, 
and  the  Law  of  Persistence  of  Mass  that  the  sum  of 
the  masses  of  the  factors  must  equal  the  sum  of  the 
masses  of  the  products.  The  sign  of  equality  may 
be  used  to  show  that  this  latter  law  holds  good  in 
a  reaction,  and  the  reaction  under  discussion  may 
be  expressed  in  the  form  of  an  equation.  Thus, 
when  the  reacting  masses  are  expressed  in  per- 
centages, we  have : 

11.19$  hydrogen  +  88. 81$  oxygen  =  100$  water, 

or,  expressing  them  as  the  weights  of  the  number 
of  liters  reacting: 

0.18^-  hydrogen  +  1.43^-  oxygen  —  i.bitf-  water  vapor, 
or,  as  parts  by  weight : 
One  part  hydrogen  +  eight  parts  oxygen  =  nine  parts  water. 


Fig.  14 APPARATUS  FOR  COLLECTING  IN  THE  SAME 

RECEIVER  THE  HYDROGEN  AND  OXYGEN  FROM  THE 
ELECTROLYSIS  OF  WATER 

The  electrodes  are  of  nickel  or  iron  and  the  water  has 
a  little  sodium  hydroxid  in  it.  The  gases  collecting 
just  below  the  stopper  can,  by  means  of  the  delivery 
tube,  be  collected  in  any  convenient  receiver  by  water 
displacement 


The  Compounds  of  Oxygen  and  Hydrogen        53 

It  is  customary  to  write  the  factors  of  an  equa- 
tion to  the  left  and  the  products  to  the  right  of  the 
equality  sign.  "  Shorthand  methods  "  of  expressing 
factors  and  products  will  be  given  later. 

An  equation  merely  expresses  the  fact  of  the 
equality  of  the  masses  of  the  factors  and  the  prod- 
ucts. It  gives  no  information  as  to  the  nature  of 
a  reaction,  and  it  does  not  tell  why  it  takes  place,  or 
what  are  the  causes  for  it.  It  is  particularly  to  be 
noted  that  a  chemical  equation  does  not  denote  an 
equality  of  volumes.  In  the  reaction  between  oxy- 
gen and  hydrogen  the  volume  of  the  product  (water) 
is  but  two-thirds  that  of  the  factors.  There  is  no  law 
of  conservation  of  volumes,  and  in  a  compound  the 
elements  are,  so  to  speak,  more  crowded  together 
than  in  the  uncombined  state. 

59.  Physical  Properties.  Water  is  an  odorless, 
tasteless  liquid.  It  is  transparent  and  colorless 
when  viewed  in  small  quantities,  but  in  large 
amounts  it  presents  a  deep  blue  or  a  green  color.  It 
is  so  common  that  its  gaseous  and  solid  states  have 
received  the  special  names  of  steam  and  ice.  Like 
all  other  pure  liquids,  it  freezes  at  a  definite  tem- 
perature, which  is  taken  as  one  of  the  fixed  points 
in  graduating  thermometers  (§  19).  Its  freezing 
point  is  but  slightly  affected  by  change  of  pressure, 
but  its  boiling  point  depends  largely  upon  the 
pressure. 

At  o°  water  has  a  vapor  tension  (§  28)  equal 
to  4.57"""-  of  mercury.  As  the  temperature  rises 
the  vapor  tension  increases  at  a  more  and  more 
rapid  rate,  until  at  100°  it  amounts  to  760""*-  of 
mercury;  i.  e.,  at  the  boiling  point  the  tension 


54  Elementary  Chemistry 

equals  the  pressure  of  the  atmosphere.  It  is  neces- 
sary, therefore,  in  giving  the  boiling  point  of  a 
liquid,  to  specify  the  pressure.  Pure  water  is  a 
very  poor  conductor  of  heat  and  electricity. 

60.  Solution.  A  substance  is  said  to  dissolve 
when,  on  being  brought  in  contact  with  a  liquid, 
a  homogeneous  mixture  is  formed.  The  liquid  is 
called  the  solvent;  the  substance  which  dissolves  in 
it,  the  solute.  Solution  is  hastened  (i)  by  using 
solids  in  condition  of  powder,  (2)  by  agitation  so  as 
to  bring  fresh  surfaces  of  solute  and  solvent  in  con- 
tact, and  (3)  usually  by  raising  the  temperature. 
The  amount  of.  a  solute  which  will  dissolve  in  a 
given  amount  of  the  solvent  depends  mainly  upon 
its  nature  and  upon  the  temperature;  crystalline 
form  and  pressure  also  have  some  slight  influence. 
When  a  solvent  refuses  to  dissolve  any  more  of  a 
substance  with  which  it  is  in  contact  at  a  certain 
temperature,  the  solution  is  said  to  be  saturated. 

A  saturated  solution  presents  a  case  of  equilib- 
rium between  the  relative  amounts  of  solvent  and 
solute.  If  the  conditions  determining  the  equilib- 
rium, as  the  temperature  and  crystalline  form,  be 
changed,  the  solubility,  or  the  amount  of  a  solute 
with  which  a  definite  amount  of  a  solvent  becomes 
saturated,  is  correspondingly  changed.  As  a  rule, 
the  solubility  of  most  solids  and  liquids  increases 
with  rise  of  temperature,  although  exceptions  are 
not  uncommon.  The  solubility  of  gases,  however, 
always  decreases  with  rise  of  temperature.  Solu- 
bilities are  usually  given  as  the  per  cent  of  the 
solute  in  the  solution  saturated  at  a  stated  temper- 
ature. 


The  Compounds  of  Oxygen  and  Hydrogen        55 

61.  Supersaturation.     If  a  saturated  solution  of 
a  solid  more  soluble  in  a  solvent  when  hot  than 
when  cold  be  prepared  at  a  higher  temperature, 
separated  perfectly  from  the  solid  (by  decantation 
or  filtration),  and  then  slowly  and  quietly  cooled 
to  a  lower  temperature,  the  cooled  solution  may 
contain   more   of  the  solute  than  is  required  for 
saturation  at  the  lower  temperature.     The  solution 
is  in  that  case  said  to  be  supersaturated.     If  a  frag- 
ment, no  matter  how  minute,  of  the  solid  solute 
be  added  to  the  solution,  the  excess  soon  crystal- 
lizes out.     Sometimes  even  a  jarring  of  the  vessel 
containing  the  solution  will  bring  about  the  same 
result.     Analogous  statements  are  true   of  gases. 
Addition  of  other  substances  will  not  relieve  the 
condition  of  supersaturation  unless  they  have  the 
same  crystalline  form  as  the  solute. 

62.  Water  of  Crystallization.      Water  enters 
into  combination  in  fixed  proportions  with  many 
substances,  forming  crystalline   compounds.     The 
union  is  but  loose,  for  the  water  may  be  expelled 
from  crystals  by  removing  the  water  vapor  from 
the   adjoining   space   or  by   heating   the   crystals 
whereby  the  tension  of  the  vapor  of  the  water  of 
crystallization  is  increased.     This  combined  water 
is  called  water  of  crystallization.     "  Burnt  alum,"  for 
instance,  is  nothing  but  ordinary  alum  deprived  of 
its  water  of  crystallization  by  heating. 

NOTE.  When  crystals  are  formed  from  solution  they  some- 
times enclose  in  little  cavities  some  of  the  liquid  (often  called 
"mother  liquor").  When  crystals  containing  such  mechanically 
enclosed  water  are  heated  the  water  vaporizes  and  the  steam 
finally  exerts  enough  pressure  to  suddenly  break  the  crystal  apart ; 
its  fragments  are  often  thrown  some  distance. 


56  Elementary  Chemistry 

63.  Efflorescence   and    Deliquescence.      When 
some  substances  containing  water  of  crystallization 
are  exposed  to  a  free  circulation  of  dry  air  they 
lose  this  "  crystal  water"  and  usually  fall  away  into 
a  powder.     Such   substances   are  said  to  effloresce. 
Certain  other  substances,  on   the   contrary,  when 
exposed  to  the  air,  take  up  water  vapor  from  it,  and 
may  absorb  enough  to  form  a  solution ;  they  are 
said  to  deliquesce. 

HYDROGEN  DIOXID 

64.  Preparation.     Cold  dilute   acids   act  upon 
metallic    peroxids    with    formation    of    hydrogen 
dioxid.     To  prepare  this  substance  in  a  state  of 
purity,   dilute   sulfuric  acid   and   barium    peroxid 
are    used,   as  the    barium    sulfate   which    is    also 
formed  is  insoluble  in  water,  and  may  be  separated 
from  the  solution  of  the  hydrogen  dioxid  by  filtra- 
tion.    The  solution  is  allowed  to  stand  over  strong 
sulfuric  acid,  which  absorbs  the  water  as  it  evap- 
orates, and  by  cooling  to  a  low  temperature,  the 
hydrogen  dioxid  may  be  made  to  crystallize. 

65.  Properties.    Physical.    Pure  hydrogen  dioxid 
forms  colorless  crystals  which  a  little  water  converts 
into  a  liquid  of  syrupy  consistence  and  an  unpleas- 
ant "metallic"  taste.     It  mixes  in  all  proportions 
with  water, 

Chemical.  Hydrogen  dioxid  decomposes  into 
water  and  oxygen  at  temperatures  above  20°.  Very 
dilute  solutions,  however,  are  quite  stable.  The 
ease  with  which  it  yields  oxygen  makes  it  a  good 
oxidizing  agent.  Under  certain  circumstances  it 
may  also  act  as  a  reducing  agent. 


T/ic  Compounds  of  Oxygen  and  Hydrogen        57 

66.  Uses.     In  dilute  solution  hydrogen  dioxid 
is  employed  in  bleaching  hair,  silk,  wool,  feathers, 
bone,  and  ivory;  as  an  antiseptic  in  surgery,  and 
as  a  tooth  wash  in  dentistry ;  also  as  a  preservative 
for  milk,  beer,  wine,  and  other  fermentable  liquids. 
Artists  use  it  to  renovate  old  paintings. 

COMPOSITION.  As  hydrogen  dioxid  cannot  be  pre- 
pared by  the  direct  union  of  its  elements,  its  composi- 
tion cannot  be  directly  determined  by  synthesis.  This 
has  been  fixed  by  analysis,  however,  as  follows  :  When 
heated  it  breaks  up  into  a  mixture  of  two  volumes  of 
water  vapor  and  one  of  oxygen.  Now,  two  volumes  of 
water  vapor  contain  two  volumes  of  hydrogen  and  one 
of  oxygen.  Hence,  hydrogen  dioxid  consists  of  equal 
volumes  of  oxygen  and  hydrogen.  Furthermore,  the 
gravimetric  analysis  of  hydrogen  dioxid  proves  it  to 
contain  sixteen  parts  of  oxygen  to  one  part  of  hydrogen. 

67.  Law  of  Multiple   Proportions.     Hydrogen 
and  oxygen  form  two  compounds.    Many  other  ele- 
ments also  unite  in  two  or  even  more  proportions 
to  form  perfectly  distinct  compounds.     For  all  such 
cases  the  Law  of  Multiple  Proportions  is  true ;  it 
may  be  stated  as  follows : 

If  two  or  more  elements  unite  to  form  two  or  more 
compounds,  the  amounts  (expressed  cither  by  weight  or 
by  volume]  of  the  element  or  elements  that  unite  with  a 
fixed  amount  of  one  element  stand  in  an  integral  (and 
usually  simple)  relation  to  one  another. 

Thus,  one  part  by  weight  of  hydrogen  combines 
with  eight  parts  of  oxygen  to  form  water,  and  with 
sixteen  parts  of  oxygen  to  form  hydrogen  dioxid, 
and  the  ratio  of  8  :  16  is  the  same  as  i  :  2.  Also  two 
volumes  of  hydrogen  combine  with  one  volume  of 
oxygen  to  form  water,  and  with  two  volumes  of 


58  Elementary  Cliemistry 

oxygen  to  form  hydrogen  dioxid ;  and  here  again 
the  ratio  is  very  simple.  Strictly  speaking,  there 
are  two  Laws  of  Multiple  Proportions,  one  having 
reference  to  mass  or  weight  and  the  other  to  vol- 
ume. The  former  is  always  applicable,  the  latter 
only  when  the  substances  are  vaporizable.  There 
can,  however,  be  but  slight  objections  to  combining 
them,  as  by  so  doing  their  similarity  is  perhaps 
rendered  the  more  evident, 

THERMOCHEMISTRY 

EXPLANATION  OF  TERMS.  When  substances  combine 
chemically,  heat  is  always  liberated  or  absorbed  ;  the 
products  become  warmer  or  colder  than  the  factors. 
The  branch  of  science  that  treats  of  these  changes  is 
called  Thermochemistry,  i,  e.,  He  at -chemistry.  Descrip- 
tive chemistry  concerns  itself  chiefly  with  changes  in 
matter;  thermo-chemistry  with  changes  in  heat  and 
chemical  energy.  The  unit  of  heat,  called  a  calory,  is 
the  amount  of  heat  required  to  change  the  temperature 
of  one  gram  of  water  one  degree. 

EXOTHERMIC  AND  ENDOTHERMIC  REACTIONS.  If  heat 
be  evolved  in  a  reaction,  it  is  said  to  be  exotJiermic, 
while  if  heat  be  absorbed  it  is  endothermic.  When  2  & 
of  hydrogen  unite  with  16^-  of  oxygen  to  form  18^-  of 
water,  68,400  calories  of  heat  are  set  free ;  the  reaction 
is  exothermic.  To  decompose  i8<r-  of  water  into  its 
elements  requires  the  expenditure  of  exactly  the  same 
amount  of  heat  energy ;  the  decomposition  of  water  is 
an  endothermic  reaction.  These  facts  may  be  expressed 
in  the  form  of  equations  as  follows  : 

iff-  hydrogen  +  i6&-  oxygen  =  18^.  'water  +  68,400  calories, 
(reacts  with)  (to  give)  (with  an  evolution  of) 

or, 

18^-  water  =  2f.  hydrogen  +  16  &•  oxygen  —  68,400  calories, 
(decomposes  into)  (and)  (with  an  absorption  of) 

Hydrogen  and  oxygen  do  not  combine  directly  to 
form  hydrogen  dioxid  so  as  to  enable  the  heat  change 


The  Compounds  of  Oxygen  and  Hydrogen        59 

to  be  measured,  but  the  compound  once  prepared  can 
easily  be  decomposed  into  its  elements  and  the  heat 
determined.  The  decomposition  of  34  f-  of  hydrogen 
dioxid  is  accompanied  with  the  evolution  of  232  calories 
of  heat.  As  the  decomposition  is  exothermic,  the  com- 
bination must  be  endothermic.  Hence, 

2ff-  hydrogen  +  32^-  oxygen  —  34^-  hydrogen  dioxid — 232  calories, 
(react  with)  (to  give)  (with  an  absorption  of) 

and 

34<?"-  hydrogen  dioxid— 1£-  hydrogen  +  32  ff-  oxygen  -f-  232  calories, 
(decomposes)  (and)  (with  an  evolution  of) 

CONSERVATION  OF  ENERGY.  The  generalization  of 
these  facts  leads  to  the  law  : 

The  amount  of  energy  manifested  in  a  reaction  is 
equal  to  that  manifested  in  the  reverse  reaction. 

Thus,  the  energy  given  out  as  heat  in  the  formation 
of  a  given  mass  of  water  is  equal  to  that  required  in  its 
decomposition.  A  mixture  of  2^-  of  hydrogen  and  16^- 
of  oxygen  contains  68,400  calories  more  heat  than  does 
i8<^-  of  water,  and  to  get  2  *"•  of  hydrogen  and  iS^-  of 
oxygen  from  water  an  amount  of  energy  equivalent  to 
68,400  calories  of  heat  must  be  put  into  the  water.  This 
is  in  accordance  with  the  Law  of  the  Conservation  of 
Energy  (§15). 

OTHER  FORMS  OF  ENERGY.  Heat  energy  is  not  the 
only  form  that  may  be  manifested  in  a  chemical 
reaction  ;  other  forms,  as  electrical,  light,  etc.,  are  often 
observed.  All  these  forms  may,  however,  be  converted 
into  each  other,  and  may  be  measured  in  the  same  units ; 
that  of  mechanical  energy,  the  erg,  is  usually  taken.  A 
calory  is  equivalent  to  4.2  million  ergs  and  the  electric 
unit  of  energy,  the/0w/r,  to  ten  million  ergs.  The  kind 
of  energy  to  be  employed  in  a  reaction  depends  upon 
its  nature.  Thus,  to  decompose  water  into  its  elements, 
such  a  high  temperature  is  required  that  it  is  ordinarily 
inconvenient  to  employ  heat  energy  in  that  case.  But 
electrical  energy  readily  effects  the  decomposition  of 
water,  and  we  shall  find  it  useful  in  many  other  reac- 
tions. The  amount  needed  to  decompose  i8^-  of  water 
is  found,  after  the  joules  in  which  it  is  measured  are 
converted  into  calories,  to  be  68,400  calories. 


60  Elementary  Chemistry 

DECOMPOSITION  AND  DISSOCIATION.  When  hydrogen 
dioxid  is  heated  it  breaks  up  into  water  and  oxygen, 
which,  when  the  temperature  is  lowered,  exhibit  but  a 
very  slight  tendency  to  re-form  the  dioxid ;  it  is  said 
to  decompose.  When  water  is  heated,  it  vaporizes  with- 
out decomposition,  but  if  the  steam  be  heated  to  a  tem- 
perature of  about  1,000°,  a  small  fraction  of  it  is  found 
to  break  up  into  uncombined  hydrogen  and  oxygen. 
With  further  rise  of  temperature  this  fraction  increases 
until,  when  the  temperature  of  about  2,800°  is  arrived 
at,  half  of  the  steam  has  been  converted  into  free 
oxygen  and  hydrogen,  and  it  is  probable  that  at  exces- 
sively high  temperatures  steam  could  not  exist  as  such, 
but  would  be  converted  into  its  constituent  gases. 

Now  it  is  found  that  on  lowering  the  temperature  the 
oxygen  and  hydrogen  reunite  to  form  steam.  At  every 
temperature  between  the  extremely  high  one  at  which 
the  elements  only  can  exist  and  about  1,000°,  there  is  a 
definite  amount  of  steam  broken  up  into  oxygen  and 
hydrogen ;  there  is  a  state  of  equilibrium  between  the 
steam  on  the  one  hand  and  the  elements,  oxygen  and 
hydrogen,  on  the  other  ;  just  as  much  steam  is  produced 
in  a  given  time  as  is  decomposed  in  the  same  time.  To 
a  decomposition  of  this  nature  the  name  of  dissociation 
has  been  assigned.  Cases  of  dissociation  are  by  no 
means  uncommon,  and  several  will  be  considered  in 
some  detail  later. 

Exercises 

/.  What  physical  constants  of  water  are  used  in  fixing  cer- 
tain units  of  measurement  ? 

2.  Why  is  it  that  insoluble  substances,  as  sand,  etc.,  have  no 
characteristic  taste  ? 

j.  How  would  you  separate  a  mixture  of  sulfur,  sand,  and 
salt,  so  as  to  obtain  all  of  each  substance  in  a  state  of  purity  ? 

4.  How  would  you  determine  the  percentage  of  water  in  an 
apple  ? 

5.  Iron  rusts  in  damp  air.     The  rust  is  a  compound  of  iron 
and  oxygen.     Where  does  the  oxygen  come  from  ?    What  gas  is 
formed  during  the  rusting  ? 

6.  How  may  a  mixture  of  hydrogen  monoxid  and  of  hydro- 
gen dioxid  be  separated  ? 


The  Compounds  of  Oxygen  and  Hydrogen        61 

Problems 

/.  If  water  contains  11.19  per  cent  of  hydrogen,  how  many 
grams  of  hydrogen  are  contained  in  3.22  g-  of  water  ? 

2.  If  3.22<?"-  of  water  contain  0.36^"-  of  hydrogen,  how  many 
grams  of  the  gas  are  contained  in  100  &•  of  water  ? 

j.  If  6.44<f-  of  water  contain  5.72  &•  of  oxygen,  how  many 
grams  of  oxygen  are  contained  in  100  £•  of  water  ? 

4.  10  c.c.  of  hydrogen  are  mixed  with  6  c.c.  of  oxygen  and 
the  mixture  exploded.  How  much  water  vapor  is  formed  and 
how  much  gas  is  left  ?  Which  gas  is  it  ? 

j.  Van  der  Plaats  in  1885  obtained  5.0834^-  of  hydrogen  by 
dissolving  20.6754  g-  of  zinc  in  dilute  sulfuric  acid.  How  many 
grams  of  water  would  be  formed  by  the  combustion  of  this  amount 
of  hydrogen,  and  what  is  the  ratio  of  the  weight  of  the  zinc  to  the 
weight  of  the  hydrogen  ? 

6.  5  I-  of  hydrogen  at  18°  and  745  mm.  are  passed  over  heated 
copper  oxid.    What  loss  in  weight  does  the  oxid  undergo  ?    What 
is  the  weight  of  the  water  formed  ? 

7.  Dumas  and  Stas  in  1843  performed  Berzelius  and  Dulong's 
experiment,  and  found  as  the  result  of  nineteen  determinations 
that  the  loss  in  weight  of  the  copper  oxid  was  840.  ^i^"-,  and  that 
945.439  ff-  of  water  were  formed.    Find  the  ratio  of  combination  of 
oxygen  to  hydrogen. 

8.  If  i l-  of  steam  at  150°  and  721.0  mm.  is  condensed  to  water 
and  the  water  totally  decomposed  by  a  current  of  electricity,  how 
many  grams  of  oxygen  and  of  hydrogen  will  be  obtained,  and  how 
many  cubic  centimeters  will  each  of  the  gases  occupy  at  23°  and 
75g  mm.  ? 

Q.  Gypsum  contains  17.65  percent  of  water  of  crystallization. 
What  volume  of  steam  at  300°  and  750  mm.  is  given  off  when  all 
the  water  of  crystallization  of  100  ff-  of  gypsum  is  expelled  ? 

10.  32.3  c.c.  of  hydrogen  at  18°  and  -]\\mm.  are  introduced 
into  a  eudiometer,  and  56. 8  c.c.  of  oxygen  at  20°  and  745  mm. 
added.  Which  gas  and  how  much  of  it  at  21°  and  745  mm.  will  be 
left  after  the  explosion,  if  the  tension  of  the  aqueous  vapor  pro- 
duced be  taken  into  account  ? 

//.  Two  volumes  of  hydrogen  dioxid  consist  of  two  volumes 
each  of  oxygen  and  of  hydrogen.  If  the  dioxid  could  be  vaporized 
without  decomposition,  what  would  be  the  weight  of  1 1-  of  it,  and 
what  would  be  its  specific  gravity  referred  to  hydrogen  ? 


CHAPTER  VI 

NITROGEN   AND   ITS   HYDROGEN 
COMPOUNDS 

HISTORICAL  NOTE.  Rutherford,  in  1772,  found  that 
when  an  animal  was  placed  in  a  confined  portion  of 
air,  a  certain  gas  incapable  of  supporting  combustion 
remained  even  after  the  carbon  dioxid  given  out  by  the 
animal  had  been  removed.  Scheele,  however,  was  the 
first  to  recognize  that  this  gas  is  a  constituent  of  the 
atmosphere.  Lavoisier  gave  the  element  the  name 
azote  (meaning  no  life),  which  it  still  bears  in  French  ; 
the  name  nitrogen  was  assigned  it  by  Chaptal,  because 
it  occurs  in  niter. 

68.  Occurrence.      Free  nitrogen    forms    about 
four-fifths  of  the  volume  of  the  atmosphere.     In 
combination  it  occurs  in  several  minerals,  as  niter 
(saltpeter)  and  Chile  saltpeter,  and  in  many  animal 
and  vegetable  substances. 

69.  Preparation.      Nitrogen  is   ordinarily  pre- 
pared by  removing  the  oxygen  from  the  air;  the 
element  is  thereby  obtained  mixed  with  a  small 
proportion   (about   one   per   cent)   of   other  gases, 
principally  argon.    The  substances  commonly  used 
to  remove  the  oxygen  are  phosphorus  and  copper, 
because  their   oxids    are    solid    and    consequently 
easily  separated  from  the  nitrogen.      Phosphorus 
set  on  fire  in  a  confined  portion  of  air  combines 
with  the  oxygen,  leaving  the  nitrogen  and  argon, 
and  if  the  operation  be  conducted  over  water,  the 
white  smoke  (phosphorus  pentoxid)  formed,  being 
very  soluble,  is  dissolved  and  thus  separated  from 

[62] 


Nitrogen  mid  its  Hydrogen  Compounds 


the  gases.  (Fig.  15.)  A  solution  of  potassium  pyro- 
gallate  will  also  absorb  the  oxygen  from  the  air. 

Nitrogen  may  be  obtained  from  certain  of  its 
compounds  free  from  argon.  Thus,  when  ammo- 
nium nitrite  or  am- 
monium  dichro- 
mate  is  heated, 
nitrogen  is  the  sole 
gaseous  product. 

70.  Properties. 
Physical.  (Table 
I.,  Appendix  D.) 
Nitrogen  is  a  color- 
less, odorless,  and 
tasteless  gas,  but 
slightly  soluble  in 
water. 

Chemical.     Nitro- 
gen combines  direct- 
ly Wltn  DUt  tew  ele-      -pig.  15  —  APPARATUS  FOR  OBTAINING  NITROGEN 
m  f^n  t  Q  At     "hi  rrli  FROM  THE  AIR  BY  BURNING  PHOSPHORUS 

temperatures  it  unites  with  some  metals,  notably 
magnesium,  forming  compounds  called  nitrids. 
Electric  sparks  passed  through  mixtures  of  oxygen 
and  nitrogen  cause  the  elements  to  unite  slowly 
(Fig-  9). 

ARGON 

HISTORICAL  NOTE.  Although  nothing  perhaps  has 
received  more  attention  chemically  than  has  the  air,  yet 
it  was  not  until  1894  that  two  English  scientists,  Ray- 
leigh  and  Ramsay,  found  that  what  had  always  been 
taken  for  pure  nitrogen  really  contained  another  ele- 
mentary gas.  This  discovery  has  been  aptly  called  the 
"triumph  of  the  third  decimal,"  for  Rayleigh  was  led 


64  Elementary  Chemistry 

to  suspect  the  presence  of  the  new  gas  in  the  air  from 
the  fact  that  the  density  of  nitrogen  from  the  atmos- 
phere differed  in  the  third  decimal  place  from  that  of 
nitrogen  prepared  from  chemical  compounds. 

PREPARATION.  When  a  series  of  electric  sparks  is 
passed  through  a  confined  portion  of  air,  the  oxygen 
and  nitrogen  gradually  unite  to  form  compounds  solu- 
ble in  water,  and  hence  easily  removed.  (Fig.  9.)  By 
admitting  enough  oxygen  to  combine  with  the  nitrogen, 
a  gaseous  residue  remains,  consisting  mainly  of  argon. 
Cavendish  performed  this  experiment  towards  the  end 
of  the  eighteenth  century,  but  did  not  examine  the  prod- 
uct carefully  and  had  no  suspicion  as  to  what  it  really 
was.  Argon  may  also  be  prepared  by  passing  pure  air, 
i.  e.,  air  containing  only  oxygen  and  nitrogen  (argon), 
over  red-hot  copper  to  remove  the  oxygen,  and  over 
red-hot  magnesium,  to  remove  the  nitrogen ;  the 
residue  is  argon. 

PROPERTIES.  Argon  is  a  colorless,  odorless,  tasteless 
gas,  somewhat  more  than  twice  as  soluble  as  nitrogen 
in  w^ater.  It  forms  no  chemical  compounds  and  may  be 
said  to  have  no  chemical  properties.  For  this  reason  its 
discoverers  gave  it  the  name  of  argon,  derived  from 
a  Greek  word  meaning  inactive. 

AMMONIA 

HISTORICAL  NOTE.  Sal  ammoniac,  a  compound  con- 
taining ammonia,  has  been  known  from  very  early 
times.  Priestley,  in  1774,  first  prepared  and  studied 
ammonia. 

71.  Occurrence.    Ammonia  is  sometimes  found 
in  very  small  amounts  in  rain  water,  it  having  been 
formed   during   thunder  storms  by  the   action   of 
lightning  on  the  hydrogen  of  water  and  the  nitro- 
gen in  the  atmosphere.     Several  of  its  compounds 
occur  in  volcanic  soils  and  in  some  animal  secretions. 

72.  Preparation.     Ammonia  is  commonly  pre- 
pared in  the  laboratory  by  the  action  of  slaked  lime 
on  some  of  its  compounds  or  by  heating  its  aqueous 


Nitrogen  and  its  Hydrogen  Compounds  65 

solution  ("ammonia  water").  It  was  formerly 
manufactured  by  heating  such  animal  substances 
as  hair,  horns,  and  hoofs  with  lime,  and  collecting 
the  gaseous  products.  Coal  used  in  the  making  of 
illuminating  gas  by  the  "old  process"  (page  91) 
gives  a  small  amount  of  ammonia,  which  is  sepa- 
rated from  the  other  gases  by  passing  their  mixture 
through  water  in  which  the  ammonia  dissolves. 
This  "  wash  water,"  when  heated  with  slaked  lime, 
gives  off  the  ammonia  it  contains. 

73.  Properties.  Physical.  Ammonia  is  a  color- 
less gas  with  a  very  pungent  odor  and  a  bitter 
taste.  It  is  extremely  soluble  in  water,  with  which 
it  combines  to  form  ammonium  hydroxid.  Several 
porous  solids,  especially  charcoal,  adsorb  large  pro- 
portions of  the  gas. 

NOTE.  To  distinguish  the  absorption  of  a  gas  by  a  liquid  from 
its  "  absorption  "  by  a  solid,  the  latter  process  is  called  adsorption 
and  the  former,  solution. 

Chemical.  Ammonia  dissociates  at  high  temper- 
atures ;  if  it  be  passed  through  a  porcelain  tube 
containing  iron  or  copper,  and  heated  to  redness, 
a  mixture  of  one  volume  of  nitrogen  to  three  of 
hydrogen  is  obtained  for  each  two  volumes  of 
ammonia  used.  While  ammonia  does  not  burn  in 
the  air,  it  does  so  when  heated  in  pure  oxygen ; 
four  volumes  of  ammonia  and  three  of  oxygen 
combine  to  form  two  volumes  of  nitrogen  and  six 
of  water  vapor.  Ozone  effects  the  immediate  oxi- 
dation of  ammonia. 

LIQUID  AMMONIA.  Faraday,  in  1823,  placed  a  little 
of  the  solid  compound  which  ammonia  forms  with 
silver  chlorid  in  the  rounded  end  of  a  stout  bent  tube 


66  Elementary  Chemistry 

(Fig.  1 6).  He  then  drew  out  the  open  end  in  a  flame 
and  sealed  it  off.  As  the  solid  compound  dissociates 
into  ammonia  and  silver  chlorid  when  heated,  the 
ammonia  gas  formed,  being  confined  in  a  relatively 
small  space,  is  subjected  to  pressure  enough  to  liquefy 
it,  especially  if  the  temperature  be  reduced  by  putting 
the  part  of  the  tube  not  containing  the  silver  compound 
in  a  freezing  mixture. 

Liquid  ammonia  is  much  used  as 
a  refrigeratory  agent  and  in  the  pro- 
duction of  artificial  ice  (Fig.  17). 
Fig.  1 6— FARADAY'S  AP-  Gaseous  ammonia  is  forced  by  a 
PARATUS  FOR  pRoouc-  compression  engine  into  a  series  of 

ING  LIQUID  AMMONIA  .  1      J     -U  a 

pipes  cooled  by  water  flowing  over 
them,  and  there  liquefied  by  pressure.  The  liquid 
ammonia  is  then  run  into  another  series  of  pipes  sur- 
rounded by  brine  and  allowed  to  expand.  The  heat 
required  to  vaporize  the  ammonia  again  is  abstracted 
from  the  brine,  which  is  thus  cooled  down  to  a  tem- 
perature of  about  —20°.  This  cold  brine  is  made  to 
circulate  in  a  system  of  pipes,  thus  lowering  the  tem- 
perature of  the  rooms  in  which  they  pass ;  by  encir- 
cling tanks  of  water  with  such  a  system  of  pipes  the 
temperature  of  the  water  is  lowered  sufficiently  to  con- 
vert it  into  ice. 

REVERSIBLE  REACTIONS  AND  CHEMICAL  EQUILIBRIUM. 
Ammonia  under  the  action  of  electric  sparks  breaks  up 
into  nitrogen  and  hydrogen  and  these  gases  under  the 
same  influence  form  ammonia.  Whether  the  reaction 
will  proceed  in  one  direction  or  the  other  depends  upon 
the  relative  masses  of  the  reacting  substances,  all  other 
conditions  remaining  the  same.  Now  it  has  been  found 
that  if  a  series  of  sparks  be  passed  through  a  mixture 
of  hydrogen  and  nitrogen  in  the  proportions  to  form 
ammonia,  after  a  time  they  will  cease  to  combine.  Also 
if  sparks  be  passed  through  ammonia,  after  a  while  it 
will  stop  dissociating.  The  composition  of  the  final 
mixtures  in  both  cases  is  found  to  be  the  same,  viz.,  2 
per  cent  of  ammonia  gas  and  98  per  cent  of  the 
mixture  of  the  gaseous  elements.  The  two  opposite 
reactions  tend  toward  the  same  state  of  equilibrium. 
The  fact  that  nitrogen  and  hydrogen  under  the  influence 


Nitrogen  and  its  Hydrogen  Compounds 

BRINE  TANK 
COLO  WATER  12° 


LL 


CONDENSER 


_r 


•15° 


^ 

lif 

_J 

1  45 

Fig.    17 — APPARATUS  FOR  PRODUCING  LIQUID  AMMONIA  FOR  REFRIGERATORY 
PURPOSES 

of  electric  sparks  tend  to  produce  ammonia  may  be 
indicated  thus  : 

Nitrogen  -f-  hydrogen  — >  ammonia 

and  that  ammonia  dissociates  into  its  constituent  ele- 
ments under  the  same  influence, 

Ammonia  — >  nitrogen  -(-  hydrogen 

the  arrows  pointing1  towards  the  product  of  the  reac- 
tion. The  two  expressions  may  be  combined  : 

Nitrogen  -f-  hydrogen  ^~*  ammonia 

The  sign  ^  expresses  very  neatly  the  nature  of  a 
reversible  reaction.  It  indicates  that  the  reaction  pro- 
ceeds both  ways,  and  also  suggests  the  equality  sign 
which  shows  that  the  Law  of  Persistence  of  Mass  is 
followed.  If  the  mixture  of  hydrogen  and  nitrogen 
be  in  just  the  proportions  to  form  ammonia  abd  is 
"sparked"  in  a  eudiometer  where  water  is  the  liquid, 
the  ammonia  will  be  dissolved  as  soon  as  formed,  and 
thus  removed  from  the  field  of  action  so  that  it  is  pos- 
sible to  make  all  of  the  mixture  combine. 


68  Elementary  Chemistry 

IMPORTANT  NUMERICAL  RELATIONSHIPS.  A  liter  of 
ammonia  at  o°  and  760  mm-  of  mercury  weighs  0.765^-, 
of  which  0.63^-  is  nitrogen  and  o.i35<?"-  is  hydrogen. 
It  is  to  be  noticed  that  these  numbers  are  in  the  inte- 
gral ratio  of  17  :  14  :  3. 

74.  Uses.  Ammonia  is  used  in  the  manufac- 
ture of  ice,  and  in  aqueous  solution  for  laundry  pur- 
poses ( "  ammonia  water  " ) ;  also  in  the  manufacture 
of  washing  soda,  anilin  dyes,  and  indigo. 

HYDRAZIN  AND  HYDRAZOIC  ACID 

HISTORICAL  NOTE.  The  elements  hydrogen  and 
nitrogen  form  besides  ammonia  three  other  compounds. 
These  do  not  occur  in  nature,  have  been  discovered 
only  in  the  last  few  years,  and  are  prepared  by  reac- 
tions too  complicated  to  be  discussed  here. 

Hydrazin  is  a  colorless  gas,  one  volume  of  which 
consists  of  two  volumes  of  hydrogen  to  one  of  nitrogen. 
It  resembles  ammonia  in  a  number  of  particulars. 

Hydrazoic  acid  is  also  a  colorless  gas,  but  has  prop- 
erties the  direct  opposite  of  those  of  ammonia  and 
hydrazin.  It  is  very  explosive  and  so  are  its  com- 
pounds. Ammonia  combines  with  it  to  form  the  fourth 
compound  of  nitrogen  and  hydrogen,  two  volumes  of 
which  contain  three  volumes  of  nitrogen  and  one  of 
hydrogen. 

Exercises 

/.  Why  was  the  name  ' '  spirits  of  hartshorn  "  formerly  applied 
to  ammonia? 

2.  What  is  the  difference  between  ammonium  hydroxid  and 
liquid  ammonia  ? 

j.  Why  does  ozone  effect  the  oxidation  of  ammonia  at  ordi- 
nary temperatures,  while  oxygen  does  not? 

4.  Given  a  jar  containing  equal  volumes  of  ammonia,  oxygen, 
and  nitrogen,  how  can  two  of  these  gases  be  re-moved  so  as  to 
leave  the  third  in  a  state  of  purity  ? 

5.  How  may  it  be  shown  experimentally  that  ammonia  con- 
sists of  nitrogen  and  hydrogen  ? 


Nitrogen  and  its  Hydrogen  Compounds  69 

Problems 

1.  If  a  liter  of  ammonia  under  standard  conditions  weighs 
o.765<?"-,  what  is  its  specific  gravity  referred  (a)  to  hydrogen,  (b) 
to  oxygen  as  a  standard  ? 

2.  What  is  the  ratio  of  the  speeds  of  transpiration  of  ammo- 
nia and  nitrogen  ? 

j.  What  volumes  of  nitrogen  and  of  hydrogen  are  required  to 
make  600  c.  c.  of  ammonia  ? 

4.  What  volume  of  oxygen  will  just  combine  with  the  hydro- 
gen obtained  by  passing  electric  sparks  through  200  c.  c.  of  ammo- 
nia until  a  state  of  equilibrium  is  arrived  at  ? 

5.  When  100  c.  c.  of  ammonia  at  18°  and  1,067  mm-  are  totally 
decomposed,  how  many  cubic  centimeters  of  nitrogen  at  22°  and 
864  tnm.  are  obtained  ? 

6.  10  &•  of  ammonia  were  passed  over  red-hot  copper.     How 
much  nitrogen  and  how  much  water  was  produced  ? 

7.  What  volume  of  nitrogen  at  25°  and  724  mm.  can  be  obtained 
from  the  decomposition  of  876  c-  c-  of  ammonia  at  20°  and  738  mm-! 

8.  265  c.  c.  of  ammonia  at  21°  and  742  mm.  were  burned  in  oxy- 
gen.    How  many  cubic  centimeters  of  nitrogen  at  18°  and  745  mm. 
were  formed  ? 

9.  A  solution  contains  18  per  cent,  by  weight,  of  ammonia. 
What  volume  of  ammonia  at  26°  and  745  mm.  will  be  obtained 
when  ii  per  cent  of  it  is  expelled  from  500  c.  c.  of  the  solution  ? 

10.  What    volume  of    oxygen   under    normal    conditions  is 
required  to  combine  with  the  hydrogen  contained  in  600  c.  c.  of 
ammonia  ? 

//.  A  sample  of  ammonium  hydroxid  contains  13  per  cent  of 
ammonia.  How  many  liters  of  ammonia  at  100°  and  748  mm.  can 
be  obtained  from  75  g-  of  the  ammonium  hydroxid  solution  ? 

12.  Ammonium  chloric!  contains  31.8  per  cent  of  ammonia. 
How  many  liters  of  ammonia  at  o°  and  760  mm.  can  be  obtained 
from  50^-  of  ammonium  chlorid? 


CHAPTER   VII 

CARBON 

75.  ^  Occurrence.     Carbon  is  very  widely  dis- 
tributed in  nature.    The  element  in  the  crystallized 
state    forms    diamond    and    graphite.     Associated 
with  organic  matter  which  has  not  been  wholly 
destroyed,  it  forms  fossil  carbon  or  coal.    Combined 
with  certain  other  elements,  principally  hydrogen, 
oxygen,  and  nitrogen,  it  is  the  essential  element  of 
all  organic  matter,  both  vegetable  and  animal. 

76.  \  General  Properties.     All  varieties  of  car- 
bon have  the  following  properties :    They  are  solids 
which  are  infusible  and  involatile  except  at  the 
highest  temperatures ;  they  are  insoluble  in  all  sol- 
vents except  some  molten  metals,  especially  iron ; 
they   are   combustible   and  yield   eleven-thirds  of 
their  own  weight  of  carbonic  acid  gas. 

77\  Diamonds,  Diamonds  owe  their  value  as 
gems  (i)  to  their  scarcity,  being  found  in  only  a 
few  places  on  the  earth,  (2)  to  their  hardness,  and 
(3)  to  their  great  brilliancy,  due  to  their  high 
refractive  index  or  power  of  bending  rays  of  light. 
Black  diamonds,  called  carbonado,  are  also  found, 
which,  while  not  used  as  gems,  are  employed  in  the 
manufacture  of  drills  for  rocks.  The  conditions 
required  for  the  formation  of  diamonds  in  nature 
seem  to  be  the  crystallization  of  molten  carbon 
under  enormous  pressure.  These  conditions  have 
been  realized  approximately  in  the  laboratory,  and 

[TO] 


Carbon  7 I 

very  small  artificial  diamonds  have  been  prepared 
in  the  following  manner :  Iron  was  melted  at  the 
high  temperature  of  the  electric  furnace  (page  115) 
and  carbon  dissolved  in  it.  When  the  mixture  was 
suddenly  cooled  by  immersing  it  in  cold  water,  a 
crust  of  solid  iron  formed,  which,  contracting  as  it 
cooled,  exerted  the  necessary  pressure.  The  iron 
was  then  dissolved  in  an  acid,  leaving  a  residue  of 
diamonds.  Diamonds  may  be  burned  by  heating 
them  in  an  atmosphere  of  oxygen.  When  heated 
away  from  oxygen  to  about  1,500°,  they  become 
changed  into  a  product  resembling  graphite. 

78.  Graphite.  Graphite  is  quite  abundantly 
diffused  over  the  earth.  It  is  also  manufactured  in 
an  electric  furnace.  If  any  variety  of  carbon  is  dis- 
solved in  molten  iron,  graphite  is  formed  when  the 
iron  cools  slowly,  and  may  be  obtained  by  dissolv- 
ing away  the  iron  in  nitric  acid. 

Graphite  has  a  grayish-black  color  and  a  metal- 
lic luster ;  hence  the  names,  black  lead  and  plumbago 
(the  Latin  word  for  lead  is  plumbum}.  It  seems  soft, 
leaves  a  black  mark  when  rubbed  over  paper,  and 
has  a  greasy  feel,  so  that  it  is  adapted  for  use  as  a 
lubricant.  It  is  a  fairly  good  conductor  of  heat  and 
electricity.  It  is  used  in  the  manufacture  of  motor 
and  dynamo  brushes,  electrodes,  conducting  sur- 
faces in  electrotyping,  paint,  stove  polish,  and 
"lead"  pencils.  For  this  last  purpose  the  graphite 
is  powdered,  mixed  with  clay,  and  the  plastic  mass 
forced  through  an  iron  cylinder  having  small  holes 
in  one  end,  from  which  it  issues  in  the  form  of 
wires.  These  are  cut  into  suitable  lengths  and 
fixed  in  grooved  sticks. 


72  Elementary  Chemistry 

Graphite  resists  the  action  of  heat  so  well  that  it 
is  used  in  making  crucibles  and  stove  polish.  It 
can  be  burned  only  at  extremely  high  temperatures 
in  an  atmosphere  of  oxygen,  or  when  heated  with 
some  oxidizing  agent,  as  potassium  chlorate. 

COAL 

79.  Occurrence.     Coal  is  found  in  a  great  many 
places;    hardly  a    country  is    entirely  without    it. 
Something  like  300,000,000  tons  are  mined  annu- 
ally, and  it  is  estimated  that  the  supply  is  sufficient 
to  cover  the  earth  with  a  layer  three  feet  thick. 

80.  Formation.    Coal  was  originally  vegetation, 
and  is  the  charred  remains  of  vast  forests  which 
covered   large   portions   of  the   earth's   surface   in 
remote   geological   ages.      Slow  subsidence  of  the 
earth's  crust  caused  these  forests  to  be  covered  with 
mud  and  sand.    The  buried  wood  decayed  slowly, 
whereby   the   volatile    compounds   formed  by  the 
decomposition  of  the   wood   escaped,   leaving   the 
involatile    portions.      Subsequent   changes   in   the 
earth's  strata  brought  it  about  that  these  coal  beds 
were  buried  deeper  and  deeper,  and  in  some  cases 
tilted  from  their  original  horizontal  position.     The 
weight  of  the  strata  above  the  coal  exerted  enor- 
mous   pressure,  so   that   it   was    compressed    into 
massive   blocks.     The   longer  this   process   lasted, 
the  purer  the  carbon.      Graphite  seems  to  be   the 
product  of  the  completed  process. 

Hard  coal  or  anthracite  may  contain  as  much  as 
90  per  cent  of  carbon,  and  bituminous  coal  up  to  70 
per  cent,  although  the  percentages  are  oftener  less. 
Even  at  the  present  time  vegetation,  especially  some 


Carbon  73 

mosses,  is  commencing  to  turn  into  coal.  Peat,  con- 
taining about  40  per  cent  of  carbon,  is  in  the  first 
stages.  Peat,  soft  coal,  and  anthracite  are  the  main 
successive  steps  in  the  decomposition  of  vegetation. 

Anthracite  is  hard,  brittle,  and  shiny,  burns  with 
almost  no  flame,  and  requires  a  high  temperature  to 
ignite  it.  It  is  much  used  in  heating  houses,  etc.,  but 
is  more  expensive  and  less  abundant  than  bituminous 
coal. 

Bituminous  coal  is  softer  and  less  shiny  than  anthra- 
cite and  ignites  at  a  lower  temperature.  It  burns  with 
a  good  deal  of  flame,  and  some  of  its  carbon  usually 
escapes  as  smoke. 

Lignite  or  brown  coal  has  been  formed  more  recently 
than  soft  coal ;  it  often  preserves  the  structure  of  the 
original  wood  and  burns  with  a  long  flame,  producing 
much  smoke. 

Jet  is  a  very  hard  and  black  variety  of  lignite  which 
takes  a  fine  polish,  and  is  used  in  making  certain  articles 
of  jewelry. 

81.  Charcoal.     The   primitive  method   of  pre- 
paring charcoal  is  by  piling  wood  in  a  conical  heap 
and  covering  it  with  earth  and  sod ;  small  openings 
are  left  so  that  just  enough  air  may  be  admitted  to 
burn  a  portion  of  the  wood,  and  thus  generate  heat 
enough  to  char  the  rest.     The  gases  formed  are 
water  vapor,  compounds  of  carbon  and  hydrogen, 
carbonic   acid,  etc.,  while  some  acetic  acid,  wood 
spirit,  and  tarry  matter  are  also  produced.     The 
finer  grades  of  charcoal,  such  as  are  used  in  the 
manufacture  of  gunpowder,  are  prepared  by  heat- 
ing wood  in  iron  retorts.     Charcoal  contains  a  little 
mineral  matter  which  was  present  in  the  wood. 

82.  Boneblack  or   Bone   Char.      Boneblack  or 
bone  char  is  obtained  bv  the  destructive  distillation 


74  Elementary  Chemistry 

of  bones.  It  is  mixed  with  a  considerable  propor- 
tion of  the  mineral  constituents  of  bones.  A  finer 
grade  is  made  by  charring-  blood. 

83.  Properties  and  Uses  of  Charcoal  and  Bone- 
black.  Charcoal  is  a  brittle  and  porous  solid  with 
neither  taste  nor  odor.  It  is  a  pretty  good  conduc- 
tor of  electricity,  but  a  poor  conductor  of  heat.  It  is 
insoluble  in  all  liquids  except  molten  iron,  and  can 
be  melted  and  vaporized  only  at  extremely  high 
temperatures.  It  resists  the  action  of  air  and  mois- 
ture very  well.  Wooden  posts  may  be  made  more 
durable  by  charring  the  surface  in  contact  with 
the  ground.  Charred  piles  have  been  found  in  a 
state  of  good  preservation  even  after  the  lapse  of 
over  2,000  years. 

Boneblack  is  usually  met  with  in  the  form  of 
black  grains. 

The  chief  use  of  charcoal  is  as  a  fuel.  It  burns 
with  almost  no  flame.  It  is  valuable  as  a  reducing 
agent,  and  is  therefore  extensively  used  in  separa- 
ting metals  from  their  ores  when  these  are  oxids. 

Charcoal  has  the  remarkable  property  of  adsorb- 
ing gases  and  condensing  them  in  its  pores.  This 
property  is  utilized  in  the  sweetening  of  foul  water 
and  tainted  meat.  To  this  property  is  to  be  ascribed 
the  deodorizing  and  disinfecting  action  of  charcoal, 
which  seems  to  be  due  to  the  oxygen  condensed  in 
the  pores  of  the  charcoal.  This  condensed  oxygen 
is  especially  active  in  combining  with  the  gases 
given  off  by  putrefying  matter.  Thus,  a  dead  ani- 
mal packed  in  charcoal  emits  no  odor,  but  its  decom- 
position is  hastened.  Charcoal  also  has  the  power 
of  removing  coloring  matters  from  solution,  but 


Carbon  75 

boneblack  is  much  superior  in  this  respect,  and  is 
extensively  used  in  sugar  refineries  to  clarify  syrups. 

84.  Lampblack.     Lampblack    is    prepared    by 
burning   pitch  or  tarry  combustibles  in  a  limited 
supply  of  oxygen  (air)  so  that  much  soot  is  formed. 
This  soot  is  conducted  into  chambers  hung  with 
sacking,  where  it  is  deposited.     Lampblack  is  used 
in  the  manufacture  of  printers'  ink,  paint,  and  shoe- 
blacking. 

85.  Coke.     When  soft  coal  is  subjected  to  de- 
structive  distillation    it   decomposes   into  volatile 
products,  from  which  illuminating  gas  and  coal  tar 
are  obtained,  and  into  an  involatile,  porous,  grayish 
residue  known  as  coke.     Coke  ignites  only  at  high 
temperatures,  burns  without  smoke  and  with  but 
little  flame,  giving  a  very  hot  fire.     It  is  used  as  a 
reducing  agent  in  the  extraction  of  metals  and  to 
a  limited  degree  for  heating  purposes. 

86.  Gas  Carbon.     Some   of  the  gaseous  com- 
pounds formed  in  the   manufacture    of  coke  are 
decomposed  on  coming  in  contact  with  the  hotter 
parts  of  the  retort,  and  the  carbon  in  them  is  depos- 
ited.    This  gas  carbon  resembles  graphite,  and  as  it 
is  a  good  conductor  of  electricity,  is  used  in  electric 
batteries  and  in  arc  lights. 

Exercises 

1.  What  property  of  carbon  in  any  of  its  forms  constitutes  its 
best  test? 

2.  Can  stove-blacking  be  used  as  shoe-blacking?    Can  shoe- 
blacking  be  used  as  stove-blacking  ? 

j>.  How  may  any  form  of  carbon  be  converted  in  part  into 
graphite  ? 

4.  The  filaments  of  incandescent  lamps  consist  of  carbon. 
What  does  the  fact  that  the  interior  of  the  bulbs  gradually 


76  Elementary  Cliemistry 

becomes  covered  with  a  dark  coating  indicate  (a)  as  to  the  tem- 
perature of  the  glowing  filament,  (6)  as  to  the  volatility  of  carbon? 

5.  Which    forms   of    carbon    occur    in    nature?    Which    are 
crystalline  ? 

6.  How  may  the  chemical  identity  of  the  various  forms  of 
the  element  carbon  be  proved  ? 

7.  Why  is  charcoal  used  in  the  lining  of  certain  makes  of 
refrigerators  ? 

8.  What  are  the  advantages  and  disadvantages  of  the  follow- 
ing fuels :  d)  hard  coal,  (2)  soft  coal,  (3)  coke,  (4)  charcoal  ? 

g.  Which  of  the  elements  thus  far  studied  occur  in  different 
allotropic  modifications  ?  Which  of  these  allotropes  are  the  most 
stable  ? 

10.  What  reducing  agents  have  been  found  among  the  various 
forms  of  the  elements  studied  ? 


CHAPTER  VIII 

THE  COMPOUNDS  OF  CARBON  WITH 
OXYGEN 

87,  Combining  of  Carbon  and  Oxygen.  When- 
ever any  form  of  carbon  is  heated  to  a  sufficiently 
high  temperature  in  air  or  oxygen,  combination 
takes  place,  accompanied  with  heat  and  light.  If 
the  oxygen  be  present  in  considerable  excess  and  if 
the  gaseous  products  be  removed  from  the  carbon 
as  fast  as  formed,  only  one  compound  of  the  two 
elements  is  produced;  this  is  variously  known  as 
^-•carbon  dioxid,  rarbonic  acid  gas,  or  Carbonic  anhydrid. 
If,  however,  the  oxygen  be  limited  in  amount,  and 
especially  if  the  products  remain  in  contact  with 
the  burning  carbon,  another  compound  named  car- 
bon monoxid  is  also  formed.  Both  these  compounds 
are  gases,  and  they  are  the  only  compounds  of  car- 
bon and  oxygen  known. 


CARBON  DIOXID 

88.  Occurrence.  Carbon  dioxid  normally  occurs 
free  in  the  atmosphere  to  the  extent  of  about  0.04 
per  cent.  The  percentage  is  higher  in  cities,  espe- 
cially near  factories  employing  steam  power,  than 
in  the  country  or  above  the  sea.  The  oxids  of  many 
metals  combine  with  carbon  dioxid  to  form  carbon- 
ates, some  of  which  form  immense  deposits,  as  lime- 
stone and  marble  (calcium  carbonate),  and  magne- 
site  (magnesium  carbonate).  Chalk,  coral,  and  the 

[77] 


78  Elementary  Chemistry 

shells  of  crustaceans  and  molluscs  are  mainly  com- 
posed of  calcium  carbonate. 

89.  Formation  and   Preparation.      Whenever 
carbon  in  any  of  its  modifications  or  any  compound 
of  carbon  is  burned  with  a  liberal  supply  of  oxygen, 
carbon  dioxid  is  formed.    It  is  also  produced  in  fer- 
mentation and  in  most  kinds  of  decay.    Formed  in 
the  tissues  of  animals,  it  is  carried  to  the  lungs  by 
the  blood  and  is  exhaled  in  respiration.     Chemical 
processes  in  the  earth's  interior  often  produce  it, 
and  the  waters  of  some  springs  are  charged  with  it. 
It  is  the   miner's   "  choke   damp,"   formed   by   the 
combustion  of  "fire  damp"  (§  102). 

The  most  convenient  way  of  preparing  carbon 
dioxid  in  a  state  of  purity  is  by  the  action  of  an  acid 
upon  a  carbonate.  With  but  few  exceptions  all 
acids  will  liberate  this  gas  from  a  carbonate. 

The  industrial  methods  of  obtaining  carbon 
dioxid  are,  (i)  the  action  of  dilute  sulfuric  acid  on 
bicarbonate  of  soda,  (2)  the  heating  of  limestone, 
(3)  the  collecting  of  the  gas  that  is  given  off  from 
the  fermenting  liquid  from  which  beer  is  made. 

90.  Properties.     Physical.    Carbon  dioxid  is  a 
colorless,  odorless  gas  with  a  rather  sharp  taste.     It 
is  much  heavier  than  air,  and  sometimes  collects  in 
hollows  of  the  ground  or  in  wells  and  cellars,  when 
it  is  produced*  more  rapidly  than  it  can  diffuse  away 
into  the  atmosphere.    There  is  a  cave  in  Italy  called 
the  "  Dog's  Cave  "  (Grotto  del  Cane)  which  is  partially 
filled  with  carbon  dioxid.     A  man  may  enter  the 
cave  with  impunity,  but  a  dog  is  promptly  suffo- 
cated.    The  reason  is,  that  the  layer  of  the  heavy 
gas  does  not  reach  up  to  a  man's  nostrils,  but  a  dog 


The  Compounds  of  Carbon   With  Oxygen         79 

is  completely  immersed  in  it.  It  is  wise  before 
entering  an  old  well  or  cellar  to  take  the  precaution 
of  lowering  into  it  a  lighted  candle  or  lantern ;  if  it 
goes  out,  carbon  dioxid  is  probably  present.  The 
gas  may  be  removed  by  introducing  powdered 
quicklime  or  ammonia,  which  absorb  it. 

At  ordinary  temperatures  carbon  dioxid  may  be 
converted  into  a  liquid  by  a  pressure  of  about  fifty 
atmospheres.  If  this  pressure  be  removed,  the  lim- 
pid, colorless  liquid  changes  into  a  gas  so  rapidly 
that,  as  heat  is  required  for  the  vaporization  of  a 
liquid,  a  portion  is  converted  into  a  white  solid, 
resembling  snow.  This  wastes  away  but  slowly 
and  may  be  handled.  It  does  not  seem  cold  to  the 
hand,  because  a  layer  of  poorly  conducting  gas  sep- 
arates it  from  the  skin.  But  if  it  be  pressed  between 
the  fingers,  it  has  the  same  effect  as  a  red-hot  iron. 

Carbon  dioxid  gas  is  somewhat  soluble  in  water ; 
at  ordinary  temperatures  a  volume  of  the  gas  dis- 
solves in  about  an  equal  volume  of  water.  With 
increase  of  pressure  there  is  an  increase  of  solu- 
bility of  the  gas. 

Chemical.  At  temperatures  above  1,300°  carbon 
dioxid  dissociates  into  oxygen  and  carbon  mo- 
noxid ;  electric  sparks  also  produce  the  same  effect. 
A  magnesium  wire  or  ribbon  ignited  in  the  air  and 
then  plunged  into  a  jar  of  carbon  dioxid  continues 
to  burn  ;  carbon  is  deposited  on  the  sides  of  the  jar. 
Carbon  dioxid  combines  with  ammonia,  lime,  and 
all  of  the  class  of  substances  known  as  hydroxids 
to  form  carbonates.  In  sunlight,  chlorophyll,  the 
green  coloring  matter  of  plants,  decomposes  car- 
bon dioxid  and  sets  oxygen  free. 


8o  Elementary  Chemistry 

91.  Uses.    The  sparkling  appearance  and  sharp 
taste  of  most  mineral  waters  are  due  to  the  carbon 
dioxid  they  hold  in  solution.    "  Soda  water  "  is  water 
charged  with   the  gas.     In   beer   and   champagne 
carbon  dioxid  is  generated  by  fermentation,  dis- 
solves  in  the  liquid,  and,  when   the  cork  of   the 
bottle  is  removed,  escapes  and  produces  the  foam- 
ing and  liveliness  of  the  liquor. 

^CARBON  MONOXID 

92.  Preparation.    Formic  acid  when  heated  with 
strong  sulfuric  acid  decomposes  into  carbon   mo- 
noxid  and  water.      It  is  more  convenient  to  use 
sodium  formiate ;  the  products  are  then  the  mo- 
noxid  and  sodium  sulfate.    Oxalic  acid  when  heated 
decomposes  into   carbon   monoxid,  carbon  dioxid, 
and  water.     As  oxalic  acid  volatilizes  somewhat  at 
the  temperature  where  the  decomposition  sets  in, 
it   is  generally  heated  with  strong   sulfuric  acid ; 
the  decomposition  then  proceeds  at  a  lower  tem- 
perature.   The  carbon  dioxid  is  removed  by  pass- 
ing the  mixture   of   gases  through  a   solution   of 
potassium  hydroxid.     The  monoxid  may   also  be 
obtained   by  heating  potassium   ferrocyanid  with 
sulfuric  acid. 

The  industrial  method  consists  in  passing  the 
gaseous  products  of  the  combustion  of  coal  over 
red-hot  coke.  The  carbon  dioxid  ivS  thus  reduced 
to  carbon  monoxid. 

93.  Properties.     Physical.     Carbon  monoxid  is 
a  colorless  and  tasteless  gas.     When  pure  its  odor 
is  scarcely  perceptible ;  it  is  very  slightly  soluble 
in  water. 


DAl'Y 


FAR AD A  V 


Plate  III 


CLAUDE  Louis  BERTHOLLET  JOSEPH  Louis  PROUST 

1748-1822;  French  1778-1850;  French 

Close  friend   and  adviser   of  Establislied  Law  of  Definite  Pro- 
Napoleon  J.     First  to  consider  portions  by  Weight.    Made  many 
the  influence  of  relative  masses  analyses  that  were  accurate  for 
on  the  nature  of  a  reaction  his  time 


JOHN  DALTON 

1766-1844;   English 

Modified  the  ancient  hypothesis 
of  atoms  to  account  for  Laws  of 
Definite  and  Multiple  Propor- 
tions, the  second  of  which  he  dis- 
covered 


MICHAEL  FARADAY  HUMPHREY  DAVY 

1791-1869;  English  1778-1829;    English 

Liquefied  ammonia,  chlorin,  and  Applied  electrolytic  methods  and 

other  gases.       Discovered   rela-  isolated   thereby  sodium,  potas- 

tionship  between  equivalents  of  sium,      calcium,     barium,     and 

elements  and  quantities  of  elec-  strontium.    Inventor  of  miners" 
tricity  lamp  bearing  his  name 


Plate  III 


The  Compounds  of  Carbon    With  Oxygen         Si 


Chemical.  Carbon  monoxid  burns  with  a  pale  blue 
flame,  forming  carbon  dioxid.  At  high  tempera- 
tures it  reduces  many  metallic  oxids. 

Physiological.  On  account  of  its  action  on  the 
blood,  carbon  monoxid  is  very  poisonous.  Haemo- 
globin, the  red  coloring  matter  of  the  blood,  com- 
bines when  in  the  lungs  with  the  oxygen  of  the 
air.  If,  however,  carbon  monoxid  be  present  in 
the  air  breathed,  it  forms  with  the  haemoglobin  a 
more  stable  compound  than  does  oxygen,  so  that 
the  blood  cannot  exercise  its  vital  functions. 

94.  Uses.  Carbon  monoxid  is  employed  as  a 
reducing  agent  in  the  manufacture  of  iron  and  steel. 

COMBUSTION  IN  A  COAL  STOVE.  When  the  draft  is 
open,  air  enters  in  abundance  at  A  (Fig.  18)  and,  com- 
bining with  the  lower  layers  of 
coal  which  are  very  hot,  forms 
carbon  dioxid.  As  this  passes 
up  through  the  hot  coal  it  is 
robbed  of  nearly  half  of  its 
oxygen,  which  combines  with 
more  coal,  so  that  carbon  mo- 
noxid is  produced.  When  this 
gas  reaches  the  top  of  the  coal 
where  plenty  of  air  is  entering 
at  Z>,  however,  it  combines  with 
the  oxygen  of  the  air,  burning 
with  a  pale  blue  flame,  and 
producing  carbon  dioxid  again. 
If  the  back  draft  at  E  be  closed, 
but  little  air  enters  at  the  stove 
door;  consequently  some  of  the 
carbon  monoxid  may  not  be 
burned  and  may  escape  into 

the  room  through  D.  Fig.  18  —  COMBUSTION  IN  A  COAL 

COMPOSITION  OF  THE  OXIDS 

OF  CARBON  ;  CARBON  DIOXID.     Lavoisier  put  some  frag- 
ments of  diamond  in  a  crucible  supported  above  a  vessel 


82  Elementary  Chemistry 

containing  mercury  and  placed  a  jar  full  of  oxygen  over 
it.  On  concentrating  the  sun's  rays  on  the  diamond  by 
means  of  a  large  lens,  he  found  it  to  gradually  disap- 
pear. After  the  apparatus  had  cooled  to  the  original 
temperature  he  observed  that  the  volume  of  the  gas 
was  the  same  as  at  first. 

Carbon  dioxid  contains  an  equal  volume  of  oxygen. 

CARBON  MONOXID.  Berth ollet  introduced  into  an 
eudiometer  ten  volumes  of  carbon  monoxid  and  ten 
volumes  of  oxygen.  After  passing  the  spark  he  found 
the  residue  to  be  composed  of  five  volumes  of  oxygen 
and  ten  volumes  of  carbon  dioxid.  Hence,  carbon 
monoxid  unites  with  half  its  volume  of  oxygen  to  form 
a  volume  of  carbon  dioxid  equal  to  the  volume  of  car- 
bon monoxid  taken.  But  carbon  dioxid  contains  its 
own  volume  of  oxygen  ;  consequently  : 

Carbon  monoxid  contains  only  half  as  much  oxygen 
as  does  the  same  volume  of  the  dioxid. 

Dumas  and  Stas  found  that  when  the  various  forms 
of  pure  carbon  were  burned  to  form  carbon  dioxid,  the 
ratio  of  the  weight  of  the  carbon  to  that  of  the  oxygen 
was  12  132,  and  Stas  determined  the  ratio  of  the  mass 
of  carbon  to  that  of  oxygen  in  carbon  monoxid  to  be 
12  :  1 6.  Carbon  dioxid  is  thus  seen  to  contain  twice 
the  mass  of  oxygen  that  the  monoxid  does. 

The  above  results  are  excellent  illustrations  both  of 
the  Laws  of  Definite  Proportions  by  Mass  and  by  Vol- 
ume, and  of  the  Law  of  Multiple  Proportions. 

SOME  NUMERICAL  .DATA.  One  liter  of  carbon  mo- 
noxid weighs  1.251  *•-,  of  which  0.715  s-  is  oxygen  and 
0.536^-  carbon.  The  weight  of  carbon  and  oxygen  in 
one  liter  of  carbon  dioxid  weighing  1.966^-  is  0.536^- 
and  1.43^-,  respectively. 

ENERGY  RELATIONSHIPS  OF  CARBON  AND  ITS  OXIDS. 
When  i2&-  of  charcoal,  graphite,  or  diamond  are  burnt 
so  as  to  produce  44  s-  of  carbon  dioxid,  the  number  of 
calories  evolved  is  97,650,  94,810,  and  94,325,  respect- 
ively. The  diamond  is  thus  seen  to  contain  less  energy 
than  graphite,  and  graphite  less  than  charcoal.  The 
allotropic  modifications  of  other  elements  also  contain 
different  amounts  of  heat  energy.  Allotropic  forms 


The  Compounds  of  Carbon    With  Oxygen         83 

differ  then  not  only  in  their  material  properties,  but 
also  in  the  amounts  of  energy  they  contain. 

It  is  impossible  to  burn  any  form  of  carbon  so  as 
to  produce  the  monoxid  without  some  admixture  of  the 
dioxid.  The  heat  of  combustion  of  carbon  monoxid 
cannot  therefore  be  determined  directly.  28^-  of  carbon 
monoxid,  however,  unite  with  i6<^-  of  oxygen  to  produce 
44<?"-  of  carbon  dioxid  with  an  evolution  of  68,170  calo- 
ries. Now,  as  in  the  combustion  of  12^-  of  charcoal  to 
44^-  of  carbon  dioxid  97,650  calories  are  given  out,  we 
find  by  subtraction  that  the  heat  effect  of  the  union  of 
charcoal  and  oxygen  to  form  carbon  monoxid  is  equal 
to  97,650  —  68,170  =  29,480  calories. 

This  procedure  illustrates  what  has  often  to  be  done 
in  measuring  the  changes  of  heat  energy  in  reactions. 
Comparatively  few  reactions  are  of  such  a  nature  that 
the  heat  evolved  or  absorbed  can  be  directly  measured. 
Usually  several  intermediate  reactions  whose  heat  effect 
is  such  as  can  be  directly  determined  have  to  be  em- 
ployed. The  investigation  of  such  cases  has  led  to  the 
discovery  of  the  Law  of  Constant  Heat  Summation,  first 
formulated  by  the  Russian,  Hess,  in  1840  : 

The  amount  of  heat  given  out  or  taken  in  by  a  system 
of  substances  undergoing  chemical  change  depends  only 
upon  the  initial  and  final  states  of  the  system. 

Thus,  carbon  may  unite  with  oxygen  to  form  the 
dioxid  in  one  of  two  ways  :  ( i)  It  may  be  burned  in  such 
a  way  that  no  carbon  monoxid  is  produced,  or  (2)  its 
combustion  may  be  attended  with  the  formation  of 
more  or  less  of  the  monoxid  which  afterward  unites 
with  oxygen  to  give  the  dioxid.  The  initial  state  of 
the  system  is  a  mixture  of  carbon  and  oxygen  the  final 
state  is  the  compound,  carbon  dioxid ;  an  intermediate 
state  may  be  a  mixture  of  both  oxids.  Now,  the  law 
affirms  that  no  matter  what  the  intermediate  states  of 
the  system,  the  heat  liberated  depends  only  upon  the 
initial  and  final  states. 

In  many  cases  a  considerable  number  of  interme- 
diate reactions  have  to  be  considered  before  a  certain 
compound  can  be  made  to  yield  the  desired  one.  The 
heat  effect  of  each  has  to  be  determined.  Simple 
algebraical  operations  then  give  the  desired  datum. 


84  Elementary  Chemistry 

Exercises 

/.  Carbon  dioxid  is  heavier  than  air.  Why  then  does  it  not 
occur  in  greater  and  greater  proportion  near  the  earth's  surface? 

2.  How  can  the  oxids  of  carbon  be  changed  the  one  into  the 
other?  What  general  processes  do  the  changes  illustrate? 

j>.  Show  how  the  oxids  of  carbon  are  an  illustration  of  the 
Laws  of  Definite  Proportions  and  of  Multiple  Proportions  both  by 
volume  and  by  weight. 

4.  What  tests  would  you  propose  for  carbon  monoxid  and  for 
carbon  dioxid  ? 

5.  How  would  you  separate  a  mixture  of  the  oxids  of  carbon  ? 

6.  Suppose  you  have  a  jar  containing  a   mixture  of  equal 
volumes  of  carbon  dioxid,  oxygen,  and  of  nitrogen.     How  can  you 
remove  two  of  the  gases  so  as  to  leave  the  third  ? 

7.  How  can  it  be  proved  experimentally  that  oxalic  acid  and 
also  formic  acid  contain  carbon  ? 

Problems 

/.  What  per  cent  by  weight  of  carbon  is  contained  in  (a)  car- 
bon monoxid  ;  (b)  carbon  dioxid  ? 

2.  How  many  times  faster  does  oxygen  diffuse  than  carbon 
dioxid  ? 

j.  How  much  water  has  to  be  decomposed  to  yield  enough 
oxygen  to  form  with  carbon  44  <?"•  of  carbon  dioxid  ? 

4.  The  annual  consumption  of  coal  in  a  certain  chemical  plant 
amounts  to  190,000  tons.     Counting  310  working  days  to  the  year, 
how  many  tons  of  carbon  dioxid  are  daily  thrown  out  into  the 
atmosphere,  if  on  an   average  the  coal  contains  70  per  cent  of 
carbon  ? 

5.  Roscoe  in  1882  obtained  on  burning  6.4406  ff-  of  diamonds, 
23.61 14  <?"•  of  carbon  dioxid.     How  much  carbon  dioxid  could  be 
obtained  from  the  burning  of  12  ff-  of  diamonds? 

6.  What  weight  of  oxygen  is  requit'ed  to  burn  a  diamond 
weighing  0.43  <?"•  and  containing  0.03  per  cent  of  an  incombustible 
impurity  ? 

7.  A  diamond  weighing  3.2678  £•  is  burned  in  oxygen,  leaving 
an  ash  amounting  to  o.ooo7<r-     What  is  the  volume  at  o°  and 
76o  mm-  of  the  carbon  dioxid  formed  ? 

8.  25  I-  of  carbon  monoxid  at  22°  and  745  mm-  are  required. 
What  volume  of  carbon  dioxid  at  18°  and  740  mm-  must  be  passed 
over  red-hot  carbon  to  yield  this  amount  of  the  monoxid  ? 


CHAPTER  IX 

SOME    NITROGEN   AND    HYDROGEN    COM- 
POUNDS OF  CARBON 

CYANOGEN 

95.  Occurrence.     Carbon  forms  but   one   com- 
pound   with   nitrogen.     This    is  called   cyanogen 
(blue  generator),  because  it  occurs  in  some  blue- 
colored  compounds. 

96.  Preparation.    Refuse  animal  matter  which 
contains  carbon  and  nitrogen,  such  as  blood  and 
horn,  is  heated  with  iron  and  potash.    The  product 
is  potassium  ferrocyanid  (yellow  prussiate  of  pot- 
ash).    When  this  is  fused  with  potassium  carbon- 
ate, potassium  cyanid  is  produced,  which  in  turn 
reacts  with  mercury  compounds  to  give  mercuric 
cyanid,    and   this    when   heated   decomposes   into 
mercury  and  cyanogen. 

97.  Properties.     Cyanogen   is  a  colorless  gas 
which  is  easily  condensed  into  a  liquid.     It  burns 
with  a  purplish  flame ;  one  volume  of  the  gas  com- 
bines with  two  volumes  of  oxygen  to  yield  two  vol- 
umes of  carbon  dioxid  and  one  volume  of  nitrogen. 
It  is  extremely  poisonous. 

HYDROCYANIC  ACID 

98.  Occurrence  and  Preparation.     Hydrocyanic 
acid  occurs  in  nature  in  combination  with  other  sub- 
stances, also  in  bitter  almonds  and  cherry  leaves. 

[35] 


86  Elementary  Chemistry 

It  is  prepared  by  the  action  of  dilute  sulfuric  acid 
on  potassium  cyanid. 

99.  Properties.    Hydrocyanic  acid  is  a  colorless, 
volatile  liquid  with  an  odor  something  like  that  of 
peach  kernels.     It  mixes  with  water  in  all  propor- 
tions, and  its  aqueous  solution  is  known  as  prussic 
acid.     It  is  one  of  the  most  deadly  of  all  known 
poisons. 

COMPOUNDS  OF  CARBON  AND  HYDROGEN; 
HYDROCARBONS 

100.  Organic  and  Inorganic  Chemistry.     Ani- 
mal and  vegetable  substances,  with  hardly  an  excep- 
tion, contain  carbon,  and  it  was  formerly  believed 
that,  except  in  a  few  cases,  carbon  compounds  could 
be   formed   only   through    the    agency   of    life    or 
"vital  force."     The   compounds   of   carbon   being 
very  numerous  and  important,  they  were  formerly 
treated  of  in  a  special  division  of  chemistry,  called 
Organic  Chemistry.     But  since  1827,  more  and  more 
carbon  compounds  have  been  prepared  artificially 
in    the   laboratory,    and    the    distinction    between 
organic  and   inorganic   chemistry   has   been   done 
away  with.     Still  it  has  been   found   advisable  to 
treat  the  compounds  of  carbon  separately,  because 
of  their  multiplicity   and    peculiar    relationships. 
The    name,    ''Organic     Chemistry,"    is    therefore 
retained,  not  to  denote  that  it  is  the  chemistry  of 
the   compounds  obtained   from  the  vegetable  and 
animal   kingdoms,  but  merely  to  indicate  that  it 
is  the  chemistry  of  the  carbon  compounds.     Some 
few  of  these  compounds,  however,  may  profitably 
be  studied  in  elementary  inorganic  chemistry. 


Nitrogen  and  Hydrogen  Compounds  of  Carbon      87 

101.  Hydrocarbons.      Hydrocarbons  are   corn- 
pounds  of  hydrogen  and  carbon.     They  are  very 
numerous  and  include  such  gases  as  acetylene  and 
methane,  such  liquids  as  kerosene  and  turpentine, 
and  the  solids,  vaseline,  paraffin,  and  so  on. 

METHANE   OR   MARSH  GAS 

102.  Occurrence.     Marsh  gas  is  one  of  the  prod- 
ucts of  the  decay  of  vegetable  matter  under  water. 
By  stirring  up  the  mud  in  marshy  places  it  may  be 
made  to  rise  to  the  surface  in  bubbles  which  also 
contain  carbon  dioxid  and  nitrogen.     Methane  fre- 
quently occurs  in  coal  mines,  probably  formed  by  a 
decomposition  of  the  coal,  and  is  there  called  "  fire 
damp." 

103.  Preparation.     Methane  is  obtained  in  the 
laboratory,  by  heating  a  mixture  of  sodium  acetate, 
sodium   or  potassium   hydroxid,  and  quicklime;  a 
little  hydrogen  and  ethylene  is  also  formed. 

104.  Properties.     Physical.     Methane  is  a  color- 
less, tasteless,  odorless  gas,  but  slightly  soluble  in 
water. 

Chemical.  Methane  burns  with  a  feebly  lumi- 
nous flame,  yielding  water  and  carbon  dioxid ;  one 
volume  of  methane  yields  one  volume  of  water  vapor 
and  one  of  carbon  dioxid.  Mixtures  of  methane 
and  oxygen  (or  air),  when  in  the  proportions  of  one 
volume  of  methane  to  two  or  three  volumes  of  oxy- 
gen (about  eight  volumes  of  air),  explode  violently 
when  ignited.  This  explosive  mixture  is  the  cause 
of  the  terrible  accidents  which  sometimes  occur  in 
coal  mines.  As  carbon  dioxid  or  "  choke  damp"  is 
formed  by  the  combustion  of  "  fire  damp,"  the 


88  Elementary  Chemistry 

miners  who  may  survive  the  explosion  usually  suc- 
cumb from  suffocation  due  to  the  former  gas. 

COMPOSITION.  If  sparks  be  made  to  strike  through 
methane  contained  in  an  eudiometer,  it  is  noticed  that 
black  particles  appear,  and  that  the  volume  of  the  gas 
increases  until  it  is  finally  twice  the  original  volume. 
An  examination  shows  that  the  particles  consist  of  amor- 
phous carbon  and  that  the  gas  is  hydrogen.  Methane 
therefore  contains  twice  its  volume  of  hydrogen.  As 
carbon  cannot  be  vaporized  readily,  its  vapor  density 
cannot  be  found,  and.  its  volume  cannot  be  compared 
with  that  of  the  methane  or  the  hydrogen.  It  may  be 
weighed,  however,  so  that  the  mass  relationships  can 
be  ascertained,  i l-  of  methane  weighs  0.716^-  and  the 
carbon  obtained  from  it,  0.536^-  As  i l-  of  hydrogen 
weighs  0.09  ^-,  we  have  the  equation  : 

\l-Qimethane        _       2  /•  of  hydrogen       _j_  carbon 

weighing  0.716^  (gives)  weighing  o.i 8of-    (and)    weighing  o. 536^. 

HEAT  OF  FORMATION  OF  METHANE.  As  hydrogen 
and  carbon  do  not  unite  directly  to  form  methane,  its 
heat  of  formation  cannot  be  determined  by  direct 
methods.  It  can,  however,  be  ascertained  by  an  appli- 
cation of  the  Law  of  Constant  Heat  Summation  (page 
83).  i6£"  of  methane  combine  with  64^-  of  oxygen  to 
produce  44^-  of  carbon  dioxid  and  36^-  of  water  with  an 
evolution  of  211,900  calories  of  heat.  We  saw  that  12  <?• 
of  carbon  (diamond)  combine  with  32  s-  of  oxygen  to 
form  44  8-  of  carbon  dioxid  with  an  evolution  of  94,320 
calories,  and  4^".  of  hydrogen  unite  with  32  s-  of  oxygen 
to  give  36^-  of  water  with  a  liberation  of  136,800  calo- 
ries. In  the  formation  of  44  <r-  of  carbon  dioxid  and  36  s- 
of  water,  there  are  required  94,320-1-136,800  =  231,120 
calories.  As  in  the  combustion  of  16  s-  of  methane 
to  these  quantities  of  water  and  carbon  dioxid,  211,900 
calories  were  liberated,  the  difference  between  the  sums 
of  the  heats  of  combustion  of  carbon  and  of  hydrogen, 
and  the  heat  of  combustion  of  methane,  must  give  the 
heat  of  formation  of  methane.  Calling  this  x,  we  have  : 

x  +  211,900  =  94,320  -f  136,800 


Nitrogen  and  Hydrogen  Compounds  of  Carbon      89 

or 

x  =  231,120  —  211,900  =  19,220 

The  heat  of  formation  of  methane  is  therefore  19,220 
calories. 

ETHYLENE    OR    OLEFIANT    GAS 

HISTORICAL  NOTE.  The  properties  of  ethylene,  dis- 
covered by  Becher  in  the  seventeenth  century,  were 
studied  by  four  Dutch  chemists  toward  the  end  of  the 
eighteenth  century.  They  gave  it  the  name  of  olefiant 
(oil-making)  gas  because  it  combines  directly  with 
chlorin  gas  to  form  an  oily  liquid,  ethylene  chlorid  or 
"  Dutch  liquor." 

105.  Preparation.     Ethylene  may  be  prepared 
by  heating   alcohol  with    strong   sulfuric    or  with 
phosphoric  acid.     It  is  also  formed  with  other  prod- 
ucts when  such  substances  as  wood  or  bituminous 
coal  are  subjected  to  destructive  distillation. 

106.  Properties.     Physical.     Ethylene  is  a  col- 
orless gas  with   a   slight  odor,  soluble  in  about  a 
sixth  its  volume  of  water. 

Chemical.  At  a  red  heat  ethylene  decomposes 
into  acetylene  and  hydrogen.  It  burns  with  a  bril- 
liant flame.  One  volume  of  ethylene  yields  two  vol- 
umes of  water  vapor  and  two  of  carbon  dioxid.  It 
is  the  chief  light-giving  constituent  of  illuminating 
gas  obtained  from  the  destructive  distillation  of 
coal. 

ACETYLENE 

107.  Preparation.     Whenever  either  ethylene 
or  the  vapor  of  alcohol  is  heated  to  redness,  some 
acetylene  is  formed.      It  may  be  prepared  from  the 
elements  by  causing  an  electric  arc  to  play  between 
two  carbon  electrodes  placed  in  an  atmosphere  of 


go  Elementary  Chemistry 

hydrogen;  this  mode  of  preparation  is  historically 
very  interesting,  as  being  one  of  the  first  direct 
syntheses  of  an  organic  compound  from  the  ele- 
ments. The  most  convenient  way  to  prepare  it  is 
by  the  action  of  water  on  calcium  carbid. 

108.  Properties.  Physical.  Acetylene  is  a  col- 
orless, tasteless  gas  of  a  faint  and  rather  pleasant 
odor  when  pure,  and  is  soluble  in  about  an  equal 
volume  of  water. 

Chemical.  When  heated  nearly  to  a  red  heat, 
acetylene  changes  into  benzene ;  six  volumes  give 
two  volumes  of  benzene  vapor.  This  peculiar  reac- 
tion, i.  e.,  this  property  it  has  of  combining  with 
itself,  is  very  characteristic.  Many  other  organic 
compounds  also  can,  under  certain  conditions, 
undergo  such  reactions,  and  the  general  phenom- 
enon is  known  as  polymerization.  Acetylene  burns 
with  a  brilliant  flame;  the  products  are  carbon 
dioxid  and  water. 

ACETYLENE  AS  AN  ILLUMINANT.  As  calcium  carbid 
can  be  made  quite  cheaply,  and  as  it  reacts  with  water 
to  give  acetylene,  this  gas,  which  burns  under  proper 
conditions  with  a  very  bright  and  agreeable  light,  has 
been  introduced  into  use  for  the  illumination  of  dwell- 
ings. Many  forms  of  generators  have  been  devised 
to  that  end.  The  safest  form  drops  the  carbid  in  small 
portions  into  the  water,  whereby  the  temperature  is 
not  raised  as  high  as  it  is  when  the  water  is  added  to 
the  carbid.  At  first  it  was  proposed  to  compress  the 
gas  into  steel  cylinders  and  to  connect  these  with  the 
gas-piping  of  a  house,  but  it  was  soon  found  that  com- 
pressed acetylene  was  highly  explosive,  so  that  such 
a  mode  of  using  it  had  to  be  abandoned.  Its  explosive^ 
ness  is  due  to  its  being  an  endothermic  compound; 
once  its  decomposition  is  started,  it  proceeds  with  explo- 
sive violence  because  of  the  energy  liberated. 


Nitrogen  and  Hydrogen  Compounds  of  Carbon     91 

109.  Methane,  Ethylene,  and  Acetylene  Com- 
pared. The  ratio  of  the  weight  of  hydrogen  to  that 
of  carbon  in  methane  is  i  :  3  ;  in  ethylene,  i  :  6 ;  and 
in  acetylene,  1:12.  The  relative  amounts  of  carbon 
are  thus  seen  to  stand  in  a  very  simple  relationship. 
The  ratios  of  the  volumes  of  hydrogen  entering 
into  the  composition  of  the  gases  are  also  very 
simple.  Thus,  two  volumes  of  methane  contain 
four  volumes  of  hydrogen ;  two  volumes  of  ethylene, 
two  of  hydrogen ;  and  two  volumes  of  acetylene, 
one  of  hydrogen.  The  less  the  proportion  of  hydro- 
gen, the  more  brilliant  and  smokier  the  flame  of 
the  hydrocarbons.  The  only  products  of  their  total 
combustion  are  carbon  dioxid  and  water. 

ILLUMINATING  GAS 

HISTORICAL  NOTE.  It  was  known  from  early  times 
that  most  vegetable  materials,  as  wood,  etc.,  when 
heated  apart  from  the  air,  yielded  gaseous  products 
burning  with  a  more  or  less  brilliant  flame,  but  it 
was  not  until  the  beginning  of  the  nineteenth  century 
that  these  gases  were  manufactured  and  distributed  by 
systems  of  pipes  for  ptirposes  of  illumination. 

MANUFACTURE  BY  THE  OLD  PROCESS.  The  manufac- 
ture of  illuminating  gas  comprises  five  more  or  less 
distinct  processes  —  the  distillation  of  the  vegetable 
material ;  the  condensation  of  the  liquid  products  car- 
ried along  by  the  gas  ;  the  washing  of  the  gas  ;  the 
purification  of  the  gas ;  the  storing  of  the  gas. 

Distillation.  Although  wood  or  petroleum  is  some- 
times used,  yet  bituminous  coal  is  by  far  the  common- 
est material  employed.  The  coal  is  placed  in  Q -shaped 
retorts  about  six  feet  in  length  made  of  fire  clay.  The 
retorts  are  arranged  in  a  furnace  as  shown  in  Fig.  19,  and 
closed  with  iron  plates  provided  with  outlets  ;  they  are 
then  heated  to  about  1,200°.  The  gaseous  and  volatile 
products  of  the  distillation  pass  oft",  leaving  the  solid 
products,  coke  and  gas  carbon,  behind. 


Nitrogen  and  Hydrogen  Compounds  of  Carbon      93 

The  volatile  products  pass  up  the  "  ascension  "  pipes, 
then  down  through  the  "  dip  "  pipes  and  bubble  through 
the  water  contained  in  the  "  hydraulic  mains,"  where  the 
less  volatile  products,  such  as  tar  and  water,  are  in  part 
condensed.  The  "  coal  tar "  which  is  thus  formed  is 
distilled  and  many  valuable  products  obtained  from  it. 

Condensation.  From  the  hydraulic  main  the  gas 
passes  into  the  "  condensers,"  a  series  of  vertical  pipes 
set  in  an  iron  box  filled  with  water.  The  temperature 
of  the  gas  is  now  much  lowered  and  most  of  the  tar, 
oils,  and  ammonia  carried  along  with  it  are  deposited. 

Washing.  To  remove  the  rest  of  the  ammonia  and 
some  of  the  carbon  dioxid  and  sulfur  compounds,  the 
gas  enters  the  base  of  a  tower  called  a  "scrubber." 
This  is  filled  with  coke,  brushwood,  or  wooden  slats,  and 
a  spray  of  water  made  to  trickle  down  it.  The  gas  is 
thus  broken  up  into  little  bubbles  and  is  thoroughly 
exposed  to  the  action  of  the  water. 

Purification.  The  impurities  which  still  remain  to 
be  removed  are  traces  of  carbon  dioxid  and  hydrogen 
sulfid,  and  the  purifying  material  is  slaked  lime  or 
some  other  material  which  absorbs  the  gases.  The 
purifying  substance  is  mixed  with  sawdust  to  make  it 
spongy  and  porous,  and  spread  out  over  trays  with  per- 
forated bottoms.  After  circulating  through  the  "  puri- 
fier," the  gas  passes  into  the  holders. 

Storage.  The  gas  holders  are  large,  bottomless 
chambers  floating  upon  a  tank  of  water,  and  secured  by 
a  framework  so  as  to  move  only  up  and  down. 

"WATER-GAS."  The  manufacture  of  illuminating 
gas  by  the  method  just  described  has  been  quite  gen- 
erally supplanted  by  the  "water-gas"  process.  When 
steam  is  passed  over  white-hot  coal,  the  former  is  par- 
tially dissociated  (page  60).  The  oxygen  then  com- 
bines with  the  carbon,  producing  carbon  monoxid,  and 
a  mixture  of  this  gas  with  hydrogen  is  the  main  prod- 
uct. This  "water-gas"  burns  with  an  almost  colorless 
flame.  It  is  used  as  a  fuel,  but  has  to  be  "  enriched  " 
with  hydrocarbons  in  order  to  make  its  flame  luminous. 
The  process  of  manufacture  is  as  follows  : 

The  "generator"  (Fig.  20)  is  charged  with  coal 
which  is  heated  as  hot  as  possible  by  means  of  a  blast  of 


Nitrogen  and  Hydrogen  Compounds  of  Carbon      9$ 

air  forced  through  it.  This  is  then  cut  off  and  steam, 
also  heated  to  a  high  temperature,  blown  through  the 
coal,  whereby  the  reaction  stated  above  takes  place. 
The  mixture  of  hydrogen  and  carbon  monoxid  is  then 
led  to  the  "  superheaters  "  in  which  low  boiling  hydro- 
carbons are  being  decomposed  so  as  to  furnish  the 
gaseous  hydrocarbons  which  impart  illuminating  power 
to  the  gas.  The  resulting  mixture  of  gases  is  then 
forced  through  the  "washer,"  "scrubber,"  and  "con- 
denser "  (these  are  essentially  the  same  as  used  in  the 
"old  process")  to  remove  any  undecomposed  liquid 
hydrocarbons  or  any  carbon  dioxid. 

PROPERTIES  OF  ILLUMINATING  GASES.  Illuminating 
gases  are  colorless,  -have  a  disagreeable  odor,  and  are  but 
very  slightly  soluble  in  water.  Water  gas  is  more  poison- 
ous than  old-process  gas  because  of  the  greater  propor- 
tion of  carbon  monoxid  it  contains.  The  analysis  of 
samples  of  these  gaseous  mixtures  gave  the  results 
recorded  in  the  following  table  : 

COMPOSITION  OF  ILLUMINATING  GASES 


Constituents 

Old 
Process 

Water 
Gas 

Hydrogen 

49-0  % 
34-5 
6.0 
7.0 
i.i 

3-5 
trace 
trace 

32.1  % 
20.  o 
12.5 
30.0 

2.6 
2.O 

trace 
trace 

Methane  

Ethylene  (and  otl 
Carbon  monoxid 
Carbon  dioxid 

ier  hydrocarbons) 

Nitrogen.. 

Ammonia 

Hydrogen  sulfid 

NATURAL  GAS.  In  numerous  localities  underground 
accumulations  of  combustible  gases  have  been  found. 
When  a  "gas  well  "  is  bored,  these  gases  rush  out  with 
great  force,  and  the  pressure  they  are  under  is  often 
sufficient  to  force  them  in  pipes  through  long  distances. 

SOME  COMMON  LIQUID  AND  SOLID  HYDROCARBONS. 
Since  1860,  petroleum  or  rock-oil  and  its  products  have 
come  into  very  general  use.  The  crude  product  is 
usually  obtained  by  boring  wells.  The  great  petroleum 
producing  regions  are  Pennsylvania,  Texas,  Baku  (Rus- 
sia), and  the  Rangoon  district  in  Burma. 


g6  Elementary  Chemistry 

Petroleum  is  a  mixture  of  substances,  the  majority 
of  which  are  hydrocarbons.  The  crude  oil  is  refined 
by  successive  treatment,  first  with  sulfuric  acid,  then 
with  caustic  potash,  and  is  finally  fractionally  distilled, 
/'.  €.,  it  is  distilled,  and  the  distillates  that  come  over 
between  certain  temperatures  are  collected  separately. 
The  most  volatile  product,  rJiigolene,  boils  at  about  18°. 
This  evaporates  so  readily  at  ordinary  temperatures  that 
it  produces  great  cold,  and  is  hence  used  as  a  refrig- 
erant. Gasoline  boils  at  about  49°,  and  is  extensively 
used  as  a  fuel,  and  in  "  gasoline  engines  "  and  lamps. 
Several  grades  of  naphthas  boiling  from  50°  to  150°  are 
separated  and  used  for  dissolving  resins  and  oils  in 
various  manufactures  and  as  fuel.  The  commercial 
names  given  to  these  light  oils  are  benzine,  petroleum 
ether,  and  ligroin.  The  product  boiling  between  150° 
and  250°  is  kerosene,  which  is  extensively  used  in 
lamps.  Other  illuminating  oils  similar  to  kerosene  are 
photogene,  solar  oil,  &&&  paraffin  oil.  These  form  inore 
than  half  of  the  petroleum.  The  mineral  or  paraffin 
lubricating  oils  boil  above  kerosene,  and  are  used  to 
lubricate  machinery.  Paraffin  is  the  last  commercial 
product;  it  is  a  white,  waxy  solid,  melting  at  about  58°, 
and  is  used  in  making  candles,  and  in  other  ways. 

Exercises 

1.  How  are  the  Laws  of  Definite  Proportions  and  Multiple 
Proportions  by  Volume  illustrated  by  the  facts  revealed  by  the 
combustion  of  methane,  ethylene,  and  acetylene  1 

2.  Given  a  mixture  of  equal  volumes  of  methane  and  carbon 
dioxid,  how  would  you  separate  the  gases  1 

j.  Given  a  compound  supposed  to  contain  carbon  and  hydro- 
gen, how  would  you  prove  the  presence  of  these  elements  1  , 

Problems 

/.  If  6  *•  of  a  mixture  of  equal  volumes  of  methane  and  ethy- 
lene are  burned,  how  many  liters  of  gas  and  what  gases  are 
formed  1 

2.  If  683  c.  c.  of  water  vapor  is  passed  over  incandescent  coke, 
and  So  per  cent  of  it  dissociated,  what  are  the  respective  volumes 
of  the  products  under  the  same  conditions  of  temperature  and 
pressure  as  the  water  vapor  1 


JUSTUS  Vox  LIEBIG  ROBERT  W.  BUNSEN 

1803-1873;  German  1811-1099;  German 

Actii'e  in  organic  and  agricnl-  Invented  the  burner,  plwtometer^ 
tural  c/ti  mistry.  Invented  con-  and  battery  bearing  Iiis  name, 
denser  bearing  his  name,  and  Invented  ivitliKirchhoff  the  spec- 
perfected  methods  cf  analyzing  troscope,  and  by  its  aid  discovered 
compounds  of  carbon  rubidium  and  caesium 


JOHANN  JACOBUS  BERZELIUS 
1799-1848  ;  Swede 

Fixed  many  equivalent  weights. 
Introduced  present-day  chemical 
symbols.  Influence  as  a  teacher 
very  marked.  Proposed  the 
dualistic  and  the  electrochemical 
theory 


ElLHARI)   MlTSCHERLICH  FRIEDRICH   WOHLER 

1794-1863;  German  1800-1882;  German 

Devised  a  method  of  estimating  Discovered  aluminum  and  beryl- 
atomic  weights  of  elements  from  Hum.    Removed  the  barrier  be- 
the  sliape  of  the  crystals  of  their  tween    organic    and    inorganic 
compounds  chemistry 


Plate  IV 


CHAPTER  X 


THE   ATMOSPHERE 

no.  Density  and  Use.  The  earth  is  sur- 
rounded by  a  gaseous  envelope  called  the  atmos- 
phere. A  limited  portion  of  it  is  usually  called  air. 
The  density  of  air  decreases  with  the  altitude  and 
it  has  been  computed  that  at  altitudes  of  100  miles 
the  density  is  less  than  that  in  the  best  vacuums 
which  man  has  as  yet  obtained.  The  atmosphere 
not  only  moderates  the  heat  of  the  sun,  but  is  also 
a  protection  against  the  cold  of  interstellar  space. 
In  it  float  the  clouds  formed  from  water  vapor 
ascending  from  earth  and  sea,  and  in  it  are  sus- 
pended dust,  smoke,  etc.  The  weight  of  the  air 
pressing  upon  the  earth's  surface  amounts  to  about 
fifteen  pounds  to  the  square  inch,  and  will  balance 
a  column  of  mercury  j6cm-  high  (page  15). 

HISTORICAL  NOTE.  Air  was  regarded  as  an  element 
before  the  eighteenth  century,  and  all  gaseous  sub- 
stances were  supposed  to  be  but  different  kinds  of  air. 
The  demonstration  that  air  is  not  an  element  but  is  a 
mixture  of  various  gases  marks  the  debut  of  modern 
chemistry.  This  fact  was  first  brought  to  light  in  1775 
by  Lavoisier  in  France  and  almost  simultaneously  by 
Scheele  in  Sweden. 

Lavoisier  heated  mercury  to  its  boiling  point  in  a 
confined  volume  of  air  ;  the  mercury  combined  with  the 
oxygen,  leaving  the  nitrogen.  His  apparatus  is  shown 
in  Fig.  21.  MMN  is  the  furnace  heating  the  flask 
whose  curved  neck  opens  under  a  jar  placed  over  a 
vessel  of  mercury.  Mercury  was  placed  in  the  flask  and 

[971 


98 


Elementary  Chemistry 


the  neck  filled  with  mercury  from  the  vessel  up  to  L ; 
a  certain  definite  volume  of  air  was  thus  confined  above 
the  mercury  in  the  flask  and  that  in  the  neck.  The 
mercury  in  the  flask  was  kept  gently  boiling  for  twelve 
days.  The  air  was  then  found  to  have  shrunk  in 
volume  from  fifty  cubic  inches  to  forty-twro  cubic 
inches.  The  red  powder  (oxid  of  mercury)  that 
appeared  on  the  surface  of  the  mercury  was  carefully 
collected  and  then  heated  to  a  higher  temperature ;  it 
gave  off  eight  cubic  inches  of  "  air  eminently  respir- 
able,"  or  oxygen,  as  Lavoisier  called  it.  The  gas  left  in 

the  flask  was  mainly 
nitrogen.  Lavoisier 
concluded  that  air  is 
composed  of  about 
four  volumes  of 
nitrogen  and  one  vol- 
ume of  oxygen,  and 
on  mixing  these 
gases  in  this  ratio,  he 
obtained  an  air  very 
similar  to  that  of  the 
atmosphere. 

Scheele  absorbed 
the  oxygen  of  the  air 

by  means  of  certain  solutions  (alkalin  sulfids) ;  his  anal- 
ysis, however,  was  less  accurate  than  that  of  Lavoisier. 

in.  Liquid  Air.  Air  was  first  liquefied  in  1877, 
but  in  very  small  amounts.  In  the  last  few  years, 
however,  methods  have  been  devised  for  obtaining 
large  amounts  of  liquid  air  with  comparative  cheap- 
ness. This  liquid  air  can  be  kept  for  some  time  in 
vessels  known  as  Dewar's  bulbs  (Fig.  22).  These 
consist  of  two  flasks  or  tubes  sealed  together  at  their 
tops,  and  the  space  between  them  made  as  perfect 
a  vacuum  as  possible.  A  vacuum  is  so  poor  a  con- 
ductor of  heat  that  the  liquid  air  can  be  shipped  long 
distances  without  any  great  amount  of  evaporation. 


Fig.  21 —LAVOISIER'S  APPARATUS  FOR  DETER- 
MINING THE  PROPORTION  OF  OXYGEN  IN  THE  AIR 


22 —  DEWAR  BULB 


The  Atmosphere  99 

The  intense  cold  readily  obtainable  by  the  aid  of 
liquid  air  permits  of  the  performance  of  many 
striking  experiments.  But  few 
practical  applications  of  liquid 
air  have  as  yet  been  developed. 

112.  Composition.  Besides 
nitrogen,  argon,  and  oxygen, 
and  very  minute  amounts  of 
hydrogen  and  helium  and  other 
gases,  air  contains  water  vapor 
and  carbon  dioxid ;  and  in  very 
small  proportions  and  in  re- 
stricted amounts,  ammonia, 
ozone,  dust,  living  and  dead 
germs.  The  first  three  elements  may  be  termed 
permanent  constituents,  as  their  proportion  varies 
but  little,  no  matter  what  the  source  of  the  air; 
the  other  constituents  vary  considerably.  The 
results  of  many  experiments  on  air  derived  from 
all  parts  of  the  earth  have  shown  that  air  contains 
about  21  per  cent  of  oxygen  (by  volume),  78  per 
cent  of  nitrogen,  and  i  per  cent  of  argon  and  other 
constituents. 

Water  is  a  most  variable  constituent.  In  cold 
and  in  desert  places  the  air  is  almost  destitute  of 
water ;  in  warm  and  wet  weather  arlcl  in  most  torrid 
climates  it  contains  much  more.  A  good  deal  of 
water  vapor  in  the  atmosphere,  i.  e.  a  high  degree 
of  humidity,  checks  the  evaporation  of  perspiration 
from  the  skin,  causing  a  sticky  and  uncomfortable 
feeling,  while  in  dry,  warm  air  evaporation  takes 
place  so  rapidly  that  the  skin  becomes  feverish  and 
the  mouth  parched.  Carbon  dioxid  is  also  quite 


IOO  Elementary  Chemistry 

variable  in  quantity ;  on  an  average,  air  contains 
0.04  per  cent.  In  crowded  rooms,  especially  if 
heated  by  lamps  or  gas,  the  amount  may  run  as 
high  as  0.3  per  cent.  If  more  than  o.i  per  cent  is 
present  the  air  should  be  regarded  as  too  impure 
to  be  fit  for  respiration. 

NOTE.  It  has  been  shown  that  hydrogen  is  a  normal  constit- 
uent of  the  air  to  the  extent  of  about  0.02  per  cent.  As  there  are 
numerous  processes  in  nature  by  which  hydrogen  is  set  free,  it  is 
believed  that  an  increase  in  the  amount  of  hydrogen  in  the  air  is 
prevented  by  its  gradually  working  its  way,  because  of  its  rapidity 
of  diffusion,  to  the  outer  limits  of  the  atmosphere  and  escaping 
into  stellar  space. 

113.  Air  Not  a  Compound.  That  air  is  not  a 
compound,  but  merely  a  mixture,  is 'proved  by  the 
following  facts : 

/.  If  air  be  dissolved  in  water  .and  the  dissolved 
air  analyzed,  it  is  found  that  it  contains  a  little  less 
than  two  volumes  of  nitrogen  to  one  of  oxygen. 
The  oxygen  is  more  soluble  than  the  nitrogen,  and 
hence  is  present  in  greater  proportion  in  the  solu- 
tion. 

2.  When  liquid  air  boils,  the  nitrogen  passes  off 
more  rapidly  than  the  oxygen,  so  that  the  residual 
liquid  becomes  richer  and  richer  in  oxygen  (page  28). 

j.  When  four^volumes  of  nitrogen  are  mixed 
with  one  of  oxygen,  the  resulting  mixture  has  all 
the  properties  of  ordinary  air,  and  yet  the  mixing 
is  accomplished  without  any  liberation  or  absorp- 
tion of  heat  or  change  of  volume,  as  would  be  the 
case  in  a  chemical  union  of  the  two  gases  (§14,  2). 

4.  When  air  is  passed  through  porous  sub- 
stances, a  partial  separation  of  the  oxygen  and 


TJie  Atmosphere  101 

nitrogen  occurs,  because  they  have  different  rates 
of  transpiration  (page  35). 

5.  Its  carbon  dioxid  may  be  separated  by  lique- 
fying the  air  and  filtering  off  the  solidified  carbon 
dioxid. 

6.  Its  water  may  be  removed  by  cooling  the  air 
below  o°. 

7.  Dust  and  other  suspended  particles  may  be 
removed  by  filtering  the  air  througn  cotton  batting. 

All  of  the  above  processes  are  of  a  physical 
nature,  and  as  a  separation  of  the  constituents  of 
the  atmosphere  can  be  effected  by  their  aid,  air  can- 
not be  a  compound. 

Perhaps  the  strongest  proof  that  air  is  not  a  com- 
pound is  the  fact  that  the  percentage  of  oxygen  it 
contains  is  variable ;  some  samples  of  air  contain 
more  than  half  a  per  cent  less  than  what  is  con- 
sidered normal  (§14,  j). 

114.  Solid  Matter  in  the  Air.  'When  sunlight 
is  admitted  into  a  dark  room  through  a  chink  in 
the  shutter,  it  streams  across  the  room  as  a  beam 
of  light  in  which  motes  may  be  seen  dancing  about. 
If  the  dust  on  the  floor  of  the  room  be  stirred  up, 
the  beam  of  light  appears  more  brilliant.  If  a 
beam  of  light  be  sent  through  a  long  and  wide 
glass  tube  smeared  on  the  inside  with  glycerin,  it 
at  first  appears  brilliant,  but  as  the  dust  is  caught 
and  held  by  the  sticky  glycerin,  it  loses  its  bril- 
liance and  finally  becomes  invisible. 

These  observations  show  that  air  is  ordinarily 
more  or  less  filled  with  solid  particles.  These  par- 
ticles are  of  quite  various  nature.  In  the  vicinity 
of  the  sea,  salt  particles  abound,  because  the  spray 


IO2  Elementary  Chemistry 

of  the  sea  is  caught  by  the  wind,  the  water  evapo- 
rated, and  the  particles  of  salt  which  were  dissolved 
in  it  are  carried  about  in  the  air.  In  cities  and 
manufacturing  districts,  smoke  particles  are  numer- 
ous. These  particles  play  an  important  part  in  the 
formation  of  rain  and  fog.  It  can  be  shown  that 
air  deprived  of  its  solid  particles  by  filtering  it 
through  cotton  wool,  cannot  form  droplets  even 
though  it  be  saturated  with  water  vapor.  These 
solid  particles  seem  to  act  as  points  or  nuclei  upon 
which  the  moisture  deposits  in  liquid  form.  The 
organic  impurities,  the  bacteria,  germs,  etc.,  which 
are  present  in  countless  numbers  in  ordinary  air 
also  play  an  important  part  in  the  fermentation 
and  putrefaction  of  plants  and  animals,  and  in  the 
communication  of  disease.  The  breathing  of  the 
same  air  over  and  over  again,  as  in  crowded  halls  or 
theaters,  produces  headache,  not  so  much  because  of 
the  diminution  of  the  oxygen  and  the  increase  of 
the  carbon  dioxid  as  because  of  the  organic  impuri- 
ties evolved  during  respiration.  The  unpleasant 
smell  noticed  on  entering  poorly  ventilated  rooms 
filled  with  people  is  also  due  to  the  same  cause. 

115.  Air  and  Life.  Each  of  the  constituents  of 
the  atmosphere  has  its  peculiar  part  to  play  in  the 
existing  order  of  things.  Animal  life  requires 
oxygen  for  its  continuance,  and  vegetable  life,  car- 
bon dioxid.  Animals  take  in  oxygen  and  give  out 
carbon  dioxid;  plants  take  in  carbon  dioxid  and 
give  out  oxygen.  A  nice  balance  between  the  two 
gases  must  be  preserved  in  the  atmosphere,  else 
life  perishes.  Nitrogen  serves  to  dilute  oxygen, 
so  that  the  chemical  activity  of  the  latter  may  be 


The  Atmosphere  103 

restrained.  With  an  atmosphere  of  nitrogen  alone, 
life  would  be  impossible ;  with  one  of  oxygen,  ani- 
mal life  would  be  so  intense  that  it  would  soon 
cease,  while  combustion  once  started  would  proceed 
with  uncontrollable  rapidity.  Water  as  cloud  and 
rain  also  has  its  part  to  play,  and  ammonia  and 
nitric  acid  help  in  the  fertilization  of  the  soil. 

Exercises 

1.  In  what  ways  is  diffusion  illustrated  by  the  atmosphere  ? 

2.  What  chemical  changes  are  produced  in  the  air  by  the 
action  of  lightning  ? 

j.  In  what  respects  does  "  atmospheric  nitrogen  "  differ  from 
nitrogen  obtained  from  a  compound  ? 

Problems 

/.  What  volumes  of  gases  will  be  left  after  6 1-  of  methane 
and  4  /•  of  air  are  made  to  unite  as  far  as  possible  ? 

2.  A  mixture  of  12.5  c.c.  of  air  and  25  c.  c.  of  hydrogen  was 
exploded,  and  the  residual  gas  found  to  measure  30.2  c.  c.  What 
per  cent  of  oxygen  did  the  air  contain  ? 

j.  Dumas  and  Boussingault  in  1841  found  16.053  &•  °f  air  to 
contain  3.18  <?"•  of  oxygen.  What  per  cent  of  oxygen  is  this  ? 

4.  If  air  on  an  average  contains  23  per  cent  by  weight  of 
oxygen,  what  is  the  per  cent  by  volume  of  the  oxygen  in  it? 

5.  10  I-  of  air  are  passed  through  a  tube  partially  filled  with 
red-hot  copper,  and  an  increase  in  its  weight  of  2.97  ff-  was  ob- 
served.    What  per  cent  of  oxygen  by  weight  is  contained  in  the 
air? 

6.  How  much  oxygen  and  nitrogen  expressed  in  percentages 
by  weight  does  a  sample  of  air  contain,  which,  according  to  Bun- 
sen,  was  made  up  of  20.96  per  cent  of  oxygen  and  79.04  per  cent 
of  nitrogen  expressed  in  percentages  by  volume  ? 

7.  (a)  How  many  liters  of  air  are  there  in  a  room  3  tn.  high, 
5  m.  long,  and  4  in-  wide  ?    (&)  How  many  liters  of  oxygen  at  o° 
and  760  mm.  does  it  contain?     (c}  How  many  grams  of  burning 
charcoal  will  completely  consume  it  if  it  burns  to  carbon  dioxid  ? 
(d)  How  many  grams  of  burning  charcoal  will  contaminate  the 
air  with  5  per  cent  of  carbon  dioxid  ? 


CHAPTER  XI 


FIRE  AND  FLAME 

116.  The  Source  of  Heat  and  Power.      The 

chemical  union  of  carbon  or  hydrogen  with  oxygen 
is  of  the  greatest  practical  importance,  as  being  the 
source  of  most  of  our  heat  and  power.  All  fuels 
contain  large  proportions  of  carbon  or  hydrogen,  or 
of  both  elements,  and  their  union  with  the  oxygen 
of  the  air  gives  out  large  amounts  of  heat.  This 
heat  may  be  utilized  to  warm  and  light  our  dwell- 
ings, cook  our  food,  drive  our  steam  engines,  and 
do  a  host  of  other  things.  The  equivalent  of  the 
heat  energy  is  pent  up,  so  to  speak,  in  the  fuel  and 
may  be  preserved  and  transported  from  place  to 
place  so  as  to  be  available  whenever  and  wherever 
it  may  be  desired.  Carbon,  hydrogen,  and  their 
compounds  are  not,  indeed,  the  only  substances 
whose  union  with  oxygen  is  accompanied  with  the 
evolution  of  much  heat  and  light,  but  so  important 
is  the  burning  of  these  two  elements,  free  or  in 
combination,  that  its  consideration  demands  special 
attention. 

117.  Combustion.     Combustion  is  the  technical 
name  for  burning.    It  signifies  a  rapid  combination 
with  oxygen.     To  express  less  rapid  combination 
with  oxygen,  as  in  respiration  and  decay,  the  ex- 
pression slow  combustion  is  employed.     The  amount 
of  heat  given  out  during  a  combustion  depends 

[104] 


Fire  and  Flame  105 

mainly  upon  the  nature  of  the  combustible,  while 
the  amount  of  light  usually  depends  upon  the 
presence  of  solid  particles  in  the  products  of  the 
combustion  and  the  rapidity  of  the  combustion.  A 
piece  of  wood  may  burn  up  in  a  few  minutes  or 
may  decay  through  ages,  but  in  both  cases  the  same 
amount  of  heat  is  given  out  and  the  products  are 
the  same,  viz.,  water,  carbon  dioxid,  and  ash. 

118.  Kindling  Temperature.  It  is  a  common 
experience  that  different  substances  have  to  be 
heated  to  different  temperatures  before  they  will 
take  fire  and  burn.  Thus,  hard  coal  has  to  be 
raised  to  a  higher  temperature  than  soft  coal  before 
it  will  catch  fire,  and  other  cases  readily  present 
themselves.  The  lowest  temperature  at  which  a 
substance  takes  fire  and  burns  is  called  its  kindling 
temperature  or  point  of  ignition. 

If  a  piece  of  wire  gauze  is  brought  down  over  a 
flame,  it  conducts  the  heat  away  so  rapidly  that  the 
gas  which  may  escape  through  the  gauze  is  cooled 
below  its  kindling  point  and  hence  does  not  catch 
fire.  Also  if  a  flame  is  enclosed  in  an  envelope  of 
wire  gauze  and  brought  into  a  gaseous  mixture 
which  would  explode  if  its  temperature  were  suffi- 
ciently raised,  no  explosion  ensues,  as  the  gauze 
mantle  distributes  and  dissipates  the  heat  so  that 
the  mixture  outside  is  not  raised  to  its  ignition 
temperature.  The  explosive  mixture  indeed  enters 
the  gauze  envelope  and  burns  quietly  therein,  but 
the  mixture  outside  does  not  take  fire. 

Prior  to  1810  explosions  in  coal  mines  were  very 
frequent ;  the  explosive  mixture  was  composed 
of  methane  (fire  damp)  and  air,  but  when  Davy 


io6 


Elementary  Chemistry 


invented  his  " safety  lamp"  (Fig.  23),  such  explo- 
sions became  impossible,  provided  the  miner  kept 
his  lamp  in  good  working  condition. 

119.  Flame.    Some  substances, 
in  burning,  merely  glow,  as  char- 
coal and  punk;  others  exhibit  the 
phenomenon  of  flame.     In  the  first 
case    the    combustibles   are    solids 
which  burn   directly,  i.  e.,  do   not 
decompose  into  other  substances  of 
a  liquid  or  gaseous  nature;   while 
in  the  second  case,  the  combusti- 
ble is  either  a  vaporizable  solid  or 
liquid,  or  a  gas,  or  decomposes  into 
vapors  or  gases  which  then  burn. 
A   flame   is  composed  of  the  hot 
gases  or  vapors  formed  during  or 
previous  to  the  combustion. 

120.  Combustible  and  Supporter 
of  Combustion.     It  is  customary  to 

consider  one  of  the  substances  taking  part  in  a 
combustion  as  the  combustible,  and  the  other  as 
the  supporter  of  the  combustion ;  the  latter  gen- 
erally surrounds  or  envelops  the  former.  In  all  the 
more  familiar  cases  of  combustion  the  air,  or  rather 
the  oxygen  it  contains,  is  regarded  as  the  supporter 
of  combustion,  and  in  ordinary  language  the  terms 
combustible  and  non-combustible  are  applied  to 
substances  which  burn  or  do  not  burn  in  air.  Also 
it  has  become  customary  to  consider  other  gases  as 
supporters  or  non-supporters  of  combustion  when 
they  behave  toward  a  combustible  as  air  does. 
These  distinctions,  though  convenient,  are  purely 


Fig.     23  —  DAVY 
"  SAFETY   LAMP" 

The  gauze  distributes 

the    heat   so    that    the 

explosive  gases  outside 

are  not  ignited 


Fire  and  Flame 


107 


arbitrary,  as  may  be  illustrated  in  the  following 
manner : 

A  large  lamp  chimney  is  fitted  at  its  lower  end  with 
a  two-hole  cork  through  which  is  passed  a  straight  tube 
of  rather  wide  bore  and  a  longer  tube  (Fig.  24).  Illumi- 
nating gas  is  passed  into  the 
chimney  through  the  longer 
tube  and  ignited  at  the  top, 
over  which  is  placed  a  piece 
of  wire  gauze.  This  creates 
a  draft  up  through  the  wide 
straight  tube,  and  the  air 
which  passes  into  the  chim- 
ney may  be  ignited  by  push- 
ing a  lighted  taper  up  the 
tube.  We  then  have  the 
spectacle  of  a  gas  burning  in 
air  and  of  air  burning  in  gas. 
It  is  evident  that  there  is 
nothing  in  the  nature  of  the 
substances  to  determine 
which  is  to  be  regarded  as 
the  combustible  and  which  as 
the  supporter  of  combustion. 
Furthermore,  since  the  ex- 
perimental conditions  deter- 
mine which  of  the  two  sub- 
stances surrounds  the  other, 
it  is  seen  that  the  terms  com- 
bustible and  non-combusti- 
ble, as  applied  to  chemical  substances,  do  not  express 
any  definite  property  of  those  substances. 

121.  Spontaneous  Combustion.  It  is  by  no 
means  a  rare  occurrence  that  conflagrations  are 
caused  by  heaps  of  combustible  substances,  espe- 
cially oil-soaked  rags  which  have  been  used  in 
cleaning  machinery,  taking  fire  of  themselves. 
Usually  in  such  cases  reactions  take  place  so  rap- 
idly that  the  heat  thereby  generated  is  sufficient  to 


Fig.  24 APPARATUS  FOR  SHOWING 

GAS  BURNING  IN  AIR  AND  AIR  BURN- 
ING IN  GAS 


io8  Elementary  Chemistry 

ignite  the  entire  mass.     Such  burning  is  said  to  be 
due  to  spontaneous  combustion. 

122.  Luminosity  of  Flame.     A  flame   is  ren- 
dered luminous  commonly  when  it  contains  solid 
particles  which  may  be   heated  to  incandescence. 
The  flame  of  burning  hydrogen  gives  out  almost 
no  light  because  neither  the  reacting  substances 
nor  the  product  of  combustion  (water)  contain  any 
solid  matter.    The  same  is  true  of  an  alcohol  flame, 
where  the  products  of  combustion  are  water  and 
carbon  dioxid.    Such  flames  may  be  rendered  lumi- 
nous by  sifting  fine  powders,  as  fine  sand  or  pow- 
dered  charcoal,  into   them.      Each    solid   particle 
becomes  heated  to  incandescence  and  thus  acts  as 
a  source  of  light.     The  flame  of  lighted  magnesium 
is  brilliant  because  the  solid  particles  of  magne- 
sium oxid  produced  become  white  hot.    The  flames 
of  wood,  candles,  and  similar  substances  are  bright 
because  they  contain  incandescent  particles  of  soot 
or  carbon.     The  oxyhydrogen  flame  can  be  made 
very  bright  by  mixing  the  vapor  of  benzine  with 
the  hydrogen  ;  benzine  contains  the  carbon  to  fur- 
nish the  necessary  solid  particles  to  produce  lumi- 
nosity. 

Luminous  flames  may  also  be  produced,  even 
when  no  solid  particles  are  present ;  thus  an  increase 
in  the  density  of  combining  gases  also  renders  the 
flame  luminous.  Highly  compressed  oxygen  and 
hydrogen  may  be  made  to  give  a  very  bright  flame. 

123.  Structure  of  Flame.     All  common  flames 
have  an  essentially  similar  structure.     Three  sep- 
arate cone-shaped  envelopes  may  be  distinguished, 
which  are  most  easily  seen  by  catching  on  white 


Fire  and  Flame  109 

paper  the  shadow  of  the  flame  placed  in  bright 
sunlight.  The  Bunsen  flame  is  an  example  of  a 
<aon-luminous  flame.  The  interior  cone  is  of  a 
greenish  color  and  gives  no  light ;  the  intermediate 
one  is  pale  blue,  and  the  exterior  a  dark  blue.  The 
candle  flame  is  an  example  of  a  luminous  flame. 
The  interior  cone  is  almost  black ;  the  interme- 
diate, yellow  and  luminous,  while  the  exterior  is 
hardly  discernible  except  at  the  base,  where  it  is 
dark  blue.  (Fig.  25.) 

The  flames  of  gases  giving  but  one  product 
of  combustion  contain  only  one  combustion  zone. 
Thus,  the  flames  of  hydrogen  and  of  carbon  mon- 
oxid,  whose  products  are  water  and  carbon  dioxid, 
respectively,  exhibit  only  one  zone. 

124.  Combustion  in  a  Candle  Flame.  The  wax, 
tallow,  or  paraffin  of  which  candles  are  made  consist 
of  substances  containing  much  carbon  and 
hydrogen.  When  the  wick  is  lighted,  the 
heat  melts  the  wax,  and  the  liquid  is  drawn 
up  the  wick  by  capillary  attraction.  It  there 
vaporizes  and  its  vapor  diffuses  toward  the 
outer  portions  of  the  flame  (Fig.  25).  The 
oxygen  of  the  air  diffuses  into  the  exterior 
and  the  intermediate  cones  where  the  tem- 
perature is  high  enough  to  cause  combustion.  STRUC- 

rr\l  1  1  •  TUREOF 

Ihe  oxygen  does  not  enter  the  inner  cone.  CANDLE 
In  the  middle  cone  the  combustion  of  the 
carbon  is  not  total,  so  that  the  incandescent  parti- 
cles there  emit  light;  these  are  burned  up  in  the 
outer  cone.  When  the  supply  of  air  is  insufficient 
or  when  there  is  a  strong  draft,  the  candle  smokes, 
i.  e.,  gives  off  unburned  carbon. 


no  Elementary  C lie  mist  ry 

125.  Smoke.     Smoke   consists  mainly  of  par- 
ticles of  unconsumed  combustible  (carbon  in  the 
form  of  soot )  mingled  with  the  gaseous  products  of 
the  combustion.     The  up-rushing  hot  gases  carry 
the  unburned  particles  out  of  the  chimney,  and  as 
the  gases  mix  with  the  air  and  become  cooled  off, 
the  particles  fall  to  the  ground.     Smoke  is  not  only 
a  nuisance,  but  is  also  a  direct  loss,  for  each  particle 
of  unburned  carbon  that  escapes  up  the  chimney 
represents  a  certain  amount  of  heat  gone  to  waste. 

SMOKE  CONSUMERS.  Smoke  consumers  are  contri- 
vances to  prevent  the  escape  into  the  air  of  any  un- 
burned combustible.  They  do  this  by  bringing  the 
unconsumed  particles  to  a  high  temperature  in  contact 
with  an  abundant  supply  of  oxygen,  whereby  complete 
combustion  is  insured.  Smoke  consumers  not  only  ren- 
der the  atmosphere  in  the  vicinity  of  places  where  much 
coal  is  used  more  healthful  and  agreeable,  but  are  also 
a  saving  to  the  user. 

126.  Temperature  of  Flames.     If  in  the  oxyhy- 
drogen  flame  all  the  heat  of  combination  were  used 
in  raising  the  temperature  of  the  water  formed,  a 
temperature  of  about  6,800°  would  be  attained.     In 
reality,  however,  the  temperature  has  been  found 
to  be  much  lower,  viz.,  2,800°.     The  reason  is  that 
the  union  is  not  complete,  and  hence  the  calculated 
value  (6,800°)  is  too  large.     It  has  been  observed 
that  at  temperatures  above  i, 000°,  water  vapor  dis- 
sociates partially  into  its  elements  (page  60).     Hy- 
drogen and  oxygen  at  temperatures  above  1,000° 
do  not  unite  completely  to  form  water ;  the  higher 
the  temperature,  the  smaller  the  amount  of  water 
vapor  formed,  and  therefore  the  less  the  heat  of 
combination.     When   hydrogen  burns,  the   great 


Fire  and  Flame  1 1 1 

heat  evolved  dissociates  the  water  partially,  and 
as  this  requires  heat,  the  temperature  is  lowered. 
Such  is  the  state  of  affairs  with  most  flames ;  the 
products  of  combustion  are  dissociated,  thus  lower- 
ing the  temperature. 

127.  Speed  of  Propagation  of  Flame.     If  any 
part  of  a  mixture  of  gases  which  are  in  the  right 
proportions  to  combine  and  whose  union  is  exo- 
thermic (page  58),  be  heated  to  the  proper  temper- 
ature, combination  ensues  and  spreads  through  the 
mixture  at  a  speed  depending  upon  the  nature  of 
the  gases.     If   a  mixture  is  combustible   (illumi- 
nating gas  and  air)  and  is  issuing  from  a  tube  at 
whose  orifice   it  may  be  ignited,  three   cases   are 
possible : 

/.  If  the  speed  of  flow  from  the  tube  is  greater 
than  the  speed  of  propagation  of  the  flame  of  the 
mixture,  it  cannot  be  ignited. 

2.  If  the  speed  of  flow  is  less  than  that  of  the 
propagation  of  the  flame,  the  gas  may  be  ignited 
and  the  flame  will  pass  back  through  the  tube. 

j.  If  the  speed  of  flow  is  about  the  same  as  the 
speed  of  propagation  the  flame  will  remain  at  the 
mouth  of  the  tube. 

The  " blowing  out"  of  a  flame  can  be  accom- 
plished only  when  the  speed  of  the  draft  of  air 
exceeds  the  speed  of  propagation  of  the  flame, 
although  the  cooling  effect  of  the  draft  has  some 
influence. 

128.  Combustion  in  a  Bunsen  Flame.     A  Bun- 
sen  burner  (Fig.  26)  consists  essentially  of  a  tube, 
at  the  base  of  which  illuminating  gas  enters  through 
a  fine  orifice, ;;/.    Just  above  the  orifice  are  openings 


112 


Elementary  Chemistry 


711 


of   adjustable   size   in   the   tube,   a.     The   gas   on 
escaping  from  the  fine  orifice  draws  in  air  from 
d  the  "  air  holes."    The  two  gases  mix 

in  the  tube  and  when  their  propor- 
tions are  properly  adjusted,  give  a 
non-luminous  flame.  If  the  speed 
of  flow  of  the  gas  is  made  less  by 
cutting  off  the  gas  supply  somewhat, 
or  if  the  speed  of  propagation  of  the 
flame  is  increased  by  heating  the 
tube  or  supplying  more  air,  the 
flame  finally  passes  back  into  the 
burner,  producing  the  phenomenon 
known  as  "  striking  back." 

THE  INCANDESCENT  GAS 
BURNER.  The  Bunsen  flame 
is  extensively  used  in  produc- 
ing the  so-called  "Welsbach 
light."  The  non-luminous 
flame  is  surrounded  by  a 
"mantle"  composed  of  a  mix- 
ture of  the  oxids  of  certain 
rare  metals  which  it  heats  to 
a  high  temperature,  thus  causing  the  mantle  to  give 
out  a  more  intense  and  steady  light  than  the  ordinary 
gas  jet. 

129.  Explosions.  Explosions  are  caused  when 
rapid  chemical  combination  takes  place  between 
substances  yielding  gaseous  products.  The  heat 
accompanying  the  reaction  raises  the  temperature 
of  the  gases  so  that  they  occupy  a  far  greater 
volume,  and  this  sudden  expansion  calls  into  action 
an  enormous  pressure.  An  explosion  is  never 
instantaneous.  It  takes  a  certain,  although  very 
small,  interval  of  time  for  the  reaction  to  spread 


Fig.   26 BUNSEN  BURNER 


Fire  and  Flame  1 1 3 

through  the  exploding  mass.  By  confining  the 
explosive  in  one  end  of  a  long  tube  and  starting 
the  reaction,  a  measurable  interval  of  time  elapses 
before  the  explosive  wave  reaches  the  other  end. 

Explosions  have  sometimes  occurred  in  flour  mills 
and  starch  factories,  due  to  the  air  in  them  being  filled 
with  a  dust  of  very  fine  flour  or  starch,  and  this  mixture 
coming  in  contact  with  a  flame.  The  ignition  of  the 
combustible  dust  started  at  one  point  flashes  through 
the  whole  mixture.  The  result  is  that  a  large  volume 
of  the  gaseous  products  of  combustion,  carbon  dioxid 
and  water  vapor,  is  suddenly  generated,  causing  an 
explosion. 

MODES  OF  ATTAINING  HIGH  TEMPERATURES.  There 
are  three  principal  modes  of  raising  the  temperature 
of  a  substance  —  (/)  by  the  concentration  of  the  sun's 
rays  ;  (2)  by  combustion  ;  (j)  by  the  electric  furnace. 

z.  The  sun's  rays  may  be  concentrated  —  brought 
to  a  focus  —  by  means  of  "burning  glasses"  (double 
convex  lens )  or  properly  placed  mirrors.  Although  the 
temperature  can  be  raised  very  high  if  large  lenses  or 
many  mirrors  are  used,  the  method  cannot  be  applied 
except  to  rather  small  bodies.  The  utilization  of  the 
sun's  rays  as  a  source  of  power  in  the  treeless  plains 
of  the  West  is  still  in  the  experimental  stage.  It  has 
its  advantages,  however,  and  it  was  the  source  of  heat 
employed  by  Priestley  which  led  to  the  discovery  of 
oxygen  (page  26);  also  by  Lavoisier  in  his  investigation 
of  the  combustibility  of  diamond. 

2.  The  commonest  method  of  getting  high  temper- 
atures is  by  means  of  the  combustion  of  fuel.  Many 
different  modes  of  doing  this  most  effectively  for  the 
purpose  in  hand  have  been  devised.  Besides  the  forms 
of  furnaces  which  are  familiar  to  every  one,  there  are 
three  other  general  types  which  are  much  used  in  the 
extraction  of  metals  from  their  ores. 

In  the  muffle  furnace  (Fig.  27)  the  substance  to  be 
heated,  the  charge,  is  enclosed  in  a  fire-clay  box  or 
retort  which  is  placed  over  the  fire  so  that  neither  the 
fuel  nor  the  fire  gases  can  enter  it. 

9 


114 


Elementary  Chemistry 


In  the  reverberatory  furnace 
(Fig.  28)  the  charge  is  placed  on 
the  bed  of  the  furnace,  the  roof 
of  which  is  given  a  slope  so  that 
the  flames  and  gases  from  the 
fire  in  the  grate  are  deflected 
down  upon  it.  The  substance  is 
spread  out  in  a  thin  layer  on  the 
bed  and  may  be  oxidized  or 
reduced  according  to  the  method 
of  firing  and  the  proportion  of 
air  admitted. 

j.  Shaft  furnaces  or  kilns 
are  either  periodic  or  continuous. 
After  the  heating  of  a  charge  in  a  periodic  furnace,  it 
is  allowed  to  cool  before  it  is  emptied  and  recharged. 
In  the  continuous  furnace,  however,  the  heated  material 
is  withdrawn  and  a  fresh  charge  added  without  loss  of 
time  or  waste  of  heat.  In  some  forms  of  continuous 
furnaces  fuel  and  material  are  added  in  alternate  lay- 
ers, while  in  others  the  fuel  is  burned  on  a  separate 
grate  and  only  the  gaseous  products  of  the  combustion 
come  in  contact  with  the  charge  in  the 
shaft.  The  construction  and  operation  of 
the  form  of  a  shaft  furnace  known  as  a 
blast  furnace  is  given  under  Iron. 


Fig.  27  —  A  MUFFLE  FURNACE 


Fig.  28  A  REVERBERATORY  FURNACE 


Fire  and  Flame 


^.  Electric  furnaces  (Fig-.  29)  consist  essentially  of  a 
receptacle  of  infusible  material  in  which  the  charge  is 
placed,  and  electrodes  pass- 
ing  through  the  furnace 
walls.  The  arc  formed  on 
the  passing  of  the  current 
is  a  center  of  intense  heat 
which  is  communicated  to 
the  charge.  In  certain 
forms  of  the  electric  fur- 
nace (Fig.  30)  the  charge 

itself  is  made  to  carry  the       Fig.  29_AN  ELECTRIC  FURNACE 
current,  and,  as  the  mate- 
rials of  which  it  is  composed  offer  great  resistance  to 
the  passage  of  the  current,  the  charge  is  heated  to  a 
very  high  temperature. 

The  introduction  of  the  electrical  furnace  into  prac- 
tical operations  has  revolutionized  some  industries  and 
created  others.  At  the  temperatures  obtainable  by  its 
use  reactions  are  made  to  occur  between  substances 
which  at  the  highest  temperature  obtained  in  combus- 
tion furnaces  are  chemically  inert  toward  each  other. 
Several  new  and  important  products,  such  as  calcium 
carbid  and  carborundum,  have  been  recently  thrown 
upon  the  market,  the  manufacture  of  which  has  been 
made  possible  only  by  the  aid  of  the  electric  furnace. 


Fig.  30 — A  RESISTANCE  FURNACE 


The  center  of  the  electro-chemical  industry  of  this 
country  is  at  Niagara  Falls,  where  large  supplies  of 
electricity  are  available  at  a  reasonable  cost. 


1 1 6  Elementary  Chemistry 

130.  Oxidizing  and  Reducing  Flames;  The 
Blowpipe.  The  outer  area  of  a  flame  contains  an 
excess  of  oxygen,  while  the  inner  region,  where 
there  is  unburnt  hydrogen  or  hydrocarbons, 
has  a  deficiency  of  oxygen.  An  oxidizable  sub- 
stance placed  in  the  outer  cone  is  converted 
into  an  oxid,  while  in  the  inner  cone  many 
oxids  are  reduced.  In  practice  these  differ- 
ent actions  of  the  two  parts  of  a  flame  are 
utilized  by  means  of  a  blowpipe.  This 
instrument  consists  essentially  of  a  tube  end- 
ing in  a  fine  jet  (Fig.  31).  For  convenience 
of  manipulation  the  jet  tube  is  usually 
placed  at  right  angles  to  the  main  part  of 
FBLGW~  the  tube.  If  the  orifice  of  the  jet  be  placed 
just  outside  the  middle  part  of  the  flame  and 
air  be  forced  through  it  from  the  lungs  or  a  bellows, 
the  oxidizing  flame  is  produced  and  may  be  directed 
upon  a  substance  held  in  a  convenient  support. 
When  the  orifice  is  placed  in  the  middle  of  a  flame 
its  reducing  part  may  be  blown  on  a  substance. 

THE  PHLOGISTON  THEORY.  The  phenomena  of  com- 
bustion are  so  striking  and  important  that  attempts 
were  early  made  to  find  a  theoretical  explanation  of  it. 
One  of  these  theories,  suggested  by  Becher  and  devel- 
oped by  Stahl,  was  dominant  for  over  a  century.  The 
theory  was  based  upon  the  hypothesis  that  a  certain 
substance  called  phlogiston  is  present  in  every  com- 
bustible, and  that  when  combustion  occurs,  this  sub- 
stance passes  off.  Easily  combustible  substances,  such 
as  charcoal  and  oils,  were  supposed  to  be  very  rich  in 
phlogiston,  while  incombustible  substances  contained 
none.  When  metals  burned  or  rusted,  they  were  said 
to  lose  phlogiston,  which  could  be  restored  to  them  by 
heating  with  charcoal.  Oxidation,  then,  was  the  result 
of  a  loss,  and  reduction,  of  a  gain  of  phlogiston. 


Fife  and  Flame  1 1/ 

According  to  this  theory,  metals  were  compounds  of 
phlogiston  and  their  "calxes, "  as  oxids  were  then 
called.  The  fact  that  the  calxes  were  heavier  than  the 
metals  themselves  was  explained  away  by  assuming 
that  phlogiston  possessed  a  sort  of  negative  gravity, 
for,  said  the  chemists  of  that  period,  when  wood  burns, 
its  smoke  ascends  and  does  not  seek  the  earth  as  heavy 
bodies  should. 

This  theory  may,  in  the  light  of  our  present  knowl- 
edge, seem  absurd,  but  it  must  not  be  forgotten  that  it 
was  believed  in  and  upheld  by  many  chemists  for  more 
than  a  century.  That  it  was  valuable  and  useful,  there 
can  be  no  doubt,  for  it  introduced  a  certain  law  and 
order  into  chemistry  which  led  to  the  discovery  of 
many  important  facts.  It  was  given  up  only  when  the 
part  that  oxygen  plays  in  combustion  was  made  clear 
by  Lavoisier  in  1783. 

Exercises 

1.  What  makes  a  lamp  smoke  ? 

2.  Why  have  large  lamps  a  powerful  central  draft  ? 
j>.     Why  is  a  candle  flame  tapering  and  conical? 

4.  Explain  how  a  flame  is  "  blown  out." 

5.  Why  is  it  that  a  mixture  of  a  gaseous  hydrocarbon  with 
air  or  oxygen  will  explode,    although  the   gas   alone   will  burn 
quietly  ? 

6.  What  relation  is  there  between  the  light  of  an  ignited 
substance  and  its  temperature? 

7.  Why  does  a  moderate  blast  of  air  help  combustion,  while 
a  strong  one  may  hinder  and  even  stop  it  ? 

8.  Why  is  the  temperature  and  consumption  of  fuel  reduced 
by  closing  the  drafts  of  a  furnace  ? 

g.  What  are  the  valuable  constituents  of  ordinary  combusti- 
bles? 

10.     Which  of  the  gases  thus  far  studied,  when  burned,  give 
out  the  most  light  ?    The  least  ? 


CHAPTER  XII 


COMBINING   AND   ELEMENTAL   WEIGHTS 

SYMBOLS,  FORMULAS,  AND  EQUATIONS 

131.  Combining  Weights.     We  have  learned 
that  elements  enter  into  combination  according  to 
definite  proportions,  both  by  weight  and  by  vol- 
ume.    Thus,  any  sample  of  pure  water  always  con- 
sists of  11.19  per  cent  of  hydrogen  and  8^.81  per 
cent  of  oxygen.     The  ratio  of  these   numbers  is 
approximately   2:16.      For   hydrogen    dioxid    the 
ratio   is   about    2  :  (2  X  16).     Likewise   ratios   were 
found  for  all  the  elements  thus  far  studied.     The 
constantly  recurring  numbers,   16  for  oxygen,    14 
for  nitrogen,   12  for  carbon,  and   i   for  hydrogen, 
stand  for  the  relative  weights  of  these  elements 
which  enter  into  combination ;  they  are  called  the 
combining  weights  of  the  elements.     Every  element 
has  a  combining  weight  which  is  as  characteristic 
of  it  as  its  color,  density,  or  any  other  property. 
These  weights  depend  for  their  numerical  values 
only  upon   what   units   of   volume   and   mass   are 
adopted. 

132.  Elemental    Weights.      In   the    following 
table  are  given  the  weights  of  a  liter  of  most  of 
the    gases    thus    far    studied,   together    with    the 
weights   of  the   elements   contained  in  a  liter  of 
their  gaseous  compounds. 

[118] 


Combining  and  Elemental  Weights 
TABLE  OF  WEIGHTS 


119 


GAS 

Weight 
in 
grams 
of  one 
liter 

Weight 
in  grams  of 
hydrogen  in 
one  liter  of 
gas 

Weight 
in  grams  of 
carbon  in 
one  liter  of 
gas 

Weight 
in  grams  of 
nitrogen  in 
one  liter  of 
gas 

Weight 
in  grams  of 
oxygen  in 
one  liter  of 
gas 

Hydrogen 

O.OQO 

2  X  O.O45 

Oxygen 

I.43O 

2  X  0.715 

Nitrogen 

I   25O 

2XO  625 

Ammonia 

o  760 

3  X  0.045 

0.625 

Steam  
Carbon  dioxid 

0.805 
1.966 

2  X  0.045 

0.536 

0.715 
2X0  715 

Carbon  monoxid 

I.25I 

0.536 

0.715 

Cyanogen 

2.322 

2  X  0.536 

2  X  0.625 

Hydrazoic  acid 

I   920 

0.045 

3  X  0.625 

Methane  .  . 

0.716 

4  X  0.045 

0.536 

Ethylene  

1.252 

4  X  0.045 

2  X  0.53*6 

Acetylene 

I    l62 

2  X  0.045 

2  X  0.536 

The  table  shows  that  the  weights  of  hydrogen, 
carbon,  nitrogen,  and  oxygen  contained  in  a  liter  of 
any  of  their  gaseous  compounds  are  0.045^-,  0.536^, 
0.625^-,  and  0.715^-,  respectively,  or  some  multiple 
of  these  weights.  These  weights  represent  the  com- 
bining proportions  of  these  elements  referred  to 
one  liter  of  their  gaseous  compounds,  and  may  be 
called  elemental  weights. 

The  elemental  weight  of  an  element  is  the  smallest 
weight  of  it  in  grams  contained  in  a  liter  of  any  of  its 
gaseous  compounds. 

Since  the  choice  of  a  liter  as  the  common  volume 
is  arbitrary,  any  other  volume  may  be  taken,  if 
there  be  sufficient  reason  for  so  doing.  If  the  vol- 
ume of  22. 2l-  be  taken,  the  elemental  weights,  which 
are  rather  inconvenient  decimal  fractions,  become 
changed  into  the  combining  weights,  which  are 
approximately  integral  numbers.  Thus,  by  multi- 
plying the  elemental  weights  by  22.2,  we  get,  on 


I2O  Elementary  Chemistry 

neglecting  the  small  fractional  parts,  the  integral 
number  of  grams  of  the  elements  contained  in 
22. 2l-  of  the  gaseous  compounds. 

0.045  X  22.2  =  (very  nearly]  i,  the  combining  weight  of  hydrogen. 
0.536X22.2=  "  "  12,  "  "  "  carbon. 

0.625X22.2=     "         "        14,    "  "       "  nitrogen. 

0.715X22.2=     "         "         16,    "  "  ""       "  oxygen. 

NOTE.  The  student  ought  perhaps  to  be  told  before  he  goes 
further  that  the  combining  weights  are  very  seldom  integral. 
Thus,  a  series  of  very  careful  analyses  and  syntheses  of  water 
has  proved  that  if  the  combining  weight  of  hydrogen  be  taken 
as  unity,  that  of  oxygen  is  15.879.  For  all  that,  the  combining 
weights  are,  with  but  few  exceptions,  so  close  to  being  integral, 
that  the  nearest  integer  may  be  taken  for  most  cases.  By  so 
doing,  the  mind  is  not  confused  by  retaining  inconvenient  num- 
bers in  memory.  The  system  of  elemental  weights  also  suffers 
under  the  disadvantage  of  consisting  of  inconvenient  numbers, 
and  as  soon  as  it  has  served  its  purpose  it  will  be  dropped. 

An  important  fact  brought  out  by  the  table  is 
that  the  weight  of  a  liter  of  hydrogen,  of  nitrogen, 
or  of  oxygen  in  the  free  state  is  double  its  ele- 
mental weight. 

J33-  Symbols.  Symbols  are  shorthand  expres- 
sions of  facts  which  facilitate  greatly  the  study  of  a 
science,  for,  by  their  use,  statements  which,  put  in 
words,  can  be  grasped  only  with  difficulty,  are  ren- 
dered much  more  easy  to  handle.  We  have  thus 
far  perhaps  not  felt  their  want  because  the  num- 
ber of  substances  studied  has  been  limited.  From 
now  on,  however,  we  shall  make  free  use  of  them. 

In  the  choice  of  symbols  two  points  should  be 
observed:  The  symbols  must  be  as  simple  as  possible  ; 
they  must  be  as  comprehensive  as  possible. 

As  symbols  of  the  chemical  elements  the  initial 
letters  of  their  names  are  taken,  and  in  case  two  or 


Combining  and  Elemental  Weights  121 

more  elements  have  names  commencing  with  the 
same  letter,  another  letter  in  the  name  is  added. 
The  symbol  of  hydrogen  is,  accordingly,  H  ;  that  of 
carbon,  C ;  that  of  nitrogen,  N ;  and  that  of  oxygen, 
O ;  while  the  symbol  of  helium  is  He ;  that  of  cad- 
mium, Cd ;  that  of  calcium,  Ca ;  that  of  nickel,  Ni ; 
that  of  osmium,  Os. 

In  some  cases  the  symbols  are  derived  from 
words  not  in  the  English  language.  Thus,  the 
German  words  for  sodium  and  for  potassium  are 
Natrium  and  Kalium,  which  in  turn  are  of  Arabic 
origin,  whence  the  symbols  Na  and  K.  The  sym- 
bols for  silver,  iron,  and  lead  are  Ag,  Fe,  and  Pb, 
derived  from  the  Latin  words  argentum,  fcrrum,  and 
plumbum.  It  is  to  be  noted  that  when  a  symbol  is 
composed  of  two  letters  the  first  is  always  a  cap- 
ital and  the  second  a  small  letter. 

Symbols  also  denote  definite  quantities  of  their 
respective  elements.  Thus,  if  hydrogen  be  taken 
as  unity,  then  H  denotes  a  unit  weight  (one  gram, 
one  pound,  one  ton,  etc.)  and  C,  N,  and  O  denote  a 
weight  12,  14,  and  16  times  this  unit  weight,  respect- 
ively. If  the  symbol  H  be  taken  to  stand  for  the 
smallest  weight  in  grams  of  hydrogen  contained  in 
a  liter  of  any  of  its  gaseous  compounds,  then  C,  N, 
and  O  represent  the  smallest  weights  in  grams,  vis., 
0.536^,  0.625^,  and  0.715^-,  respectively,  that  can 
exist  in  a  liter  of  any  of  their  gaseous  compounds. 
H,  C,  N,  and  O  may  represent  the  combining 
weights,  the  elemental  weights,  or  any  other  corre- 
sponding set  of  weights,  for  such  sets  of  weights 
are  ratios  and  depend  for  their  value  only  upon 
what  weight  is  taken  as  a  standard. 


122  Elementary  Chemistry 

134.  Formulas.    By  writing  the  symbols  com- 
posing a  compound  one  after  another  and  by  indi- 
cating with  a  subscript  (also  called  sub-figure)  the 
number  of  times  a  symbol  occurs,  the  formula  of  a 
compound  is  obtained.     The   order   in  which   the 
symbols  is  written  is  immaterial,  although  there  is 
usually  some  customary  or  preferred  order.     The 
subscript  refers  only  to  the  symbol  under  which  it 
is  written.     Often  two  or  more  symbols  are  written 
in  parentheses  with  a  subscript,  the  subscript  then 
referring  to  all  the  symbols  within  the  parentheses. 
Thus,  the  formulas,  CaO2H2  and  Ca(OH)2  stand  for 
the  same  compound,  calcium  hydroxid ;  the  second 
mode  of  expression  is  preferred  for  reasons  given 
below.     When  a  number  is  written  before  a  for- 
mula, it  has  the  same  effect  as  a  coefficient  in  alge- 
bra, and  multiplies  all  the  symbols  in  the  formula. 
Thus,  5  Ca(OH)2  indicates  five  symbols  of  calcium 
and  ten  each  of  oxygen  and  hydrogen. 

135.  Radicals.    There  are  many  groups  of  ele- 
ments which  seem  to  hold  together  in  most  chem- 
ical reactions,  but   which  cannot  be  isolated  as  a 
definite  compound.   Such  groups  are  called  radicals. 
Thus,  the  OH  in  the  formula  Ca(OH)2  is  an  impor- 
tant radical  named  hydroxyl,  a  word  recalling  the 
elements  of  which  it  is  composed  —  hydro,  an  abbre- 
viation of  hydrogen,  and  oxyl,  one  of  oxygen.     An- 
other important  radical  is  ammonium,  NH4.     The 
formula  for  ammonium  hydroxid  is  written  NH4OH 
and  not  NH5O,  so  as  to  emphasize  the  fact  that  it 
consists  of  the  radicals,  ammonium  and  hydroxyl. 
When  a  radical  occurs  more  than  once  in  a  formula 
it  is  usually  enclosed  in  parenthesis ;  for  example, 


Combining  and  Elemental  Weights  123 

Ca(OH)2,  calcium  hydroxid,  and  ammonium  car- 
bonate, (NH4)2CO3. 

136.  Formulas;  Combining  and  Elemental 
Weights.  When  the  weights  of  the  constituent 
elements  in  a  definite  volume  of  a  gaseous  com- 
pound are  known,  the  formula  of  the  compound 
can  be  readily  established.  To  illustrate,  one  liter 
of  ammonia  contains  0.625^-  of  nitrogen  and 
3  X  0.045^-  of  hydrogen.  (Cf.  table,  §  132.)  It  con- 
tains one  elemental  weight  of  nitrogen  and  three  of 
hydrogen,  and  inasmuch  as  the  symbols  stand  for 
these  elemental  weights,  the  formula  of  ammonia 
is  seen  to  be  NH3.  One  liter  of  methane  contains 
0.536^-  of  carbon  and  4  X  0.045^-  of  hydrogen;  its 
formula  is  therefore  CH4 .  In  a  liter  of  water  vapor 
there  are  0.71 5  ^  of  oxygen  and  2  X  0.045  *"•  of  hydro- 
gen, and  its  formula  is  H2O.  One  liter  of  carbon 
monoxid  contains  0.536^-  of  carbon  and  0.715^-  of 
oxygen,  and  one  liter  of  carbon  dioxid  contains 
0.536^-  of  carbon  and  2  X  0.715^-  of  oxygen;  hence 
their  formulas  are  CO  and  CO  2,  respectively. 

Similarly,  formulas  for  the  free  elements  may 
be  found.  A  liter  of  hydrogen  weighs  2  X  0.045  g'->  so 
that  its  formula  is  H2.  The  formulas  for  free  nitro- 
gen and  oxygen  are  N2  and  O2,  respectively,  since 
a  liter  of  either  gas  weighs  twice  as  much  as  the 
smallest  weight  of  it  in  grams  contained  in  a  liter 
of  any  of  its  gaseous  compounds.  Also,  by  indirect 
methods,  the  weight  of  a  liter  of  ozone  has  been 
estimated  to  be  3  X  0.715^,  making  its  formula  O3. 

In  like  manner  the  formula  of  a  compound 
may  be  established  by  considering  the  combining 
weights,  i.  e.,  the  weights  in  grams  of  the  elements 


124  Elementary  Chemistry 

contained  in  22.2 /  of  the  compound.  22.2  L  of  ethy- 
lene  contain  2  X  1 2  *•  of  carbon  and  4  X  i  g-  of  hydro- 
gen; hence  its  formula  is  C2H4.  The  formula  of 
acetylene  is  C2H2,  because  22.2  7-  of  it  are  made  up 
of  2  X  12*"-  of  carbon  and  2  X  i  ^  of  hydrogen.  22.2  L 
of  nitrogen  weigh  28^-;  hence  its  formula  is  N2. 

It  is  to  be  carefully  noted  that  a  formula  repre- 
sents a  definite  volume  of  a  substance  in  the  gas- 
eous state.  Thus,  in  the  system  of  elemental 
weights,  the  formulas  stand  for  one  liter  of  the  gas ; 
in  the  system  of  combining  weights,  for  22. 2  L. 

137.  What  a  Formula  Means.  A  formula 
expresses  the  following  facts  in  regard  to  a  com- 
pound : 

/.     It  shows  what  elements  a  compound  contains. 

2.  It  specifies  what  are  the  weights  of  each  of 
the  component  elements  in  a  given  volume  of  a 
gaseous  compound.  For  example,  the  formula  of 
ammonia,  NH3,  shows  that  one  liter  of  the  gas 
represented  by  that  formula  weighs  0.76^-,  for  the 
sum  of  the  elemental  weights  of  its  constituent  ele- 
ments is  0.625  -f  (3  X  0.045)  —  0-76. 

j.     It  indicates  the  ratio  of  the  weights  of  the 
component   elements,  from  which  the   percentage 
composition   may  be   calculated.     Thus,  a   liter  of 
water  vapor  contains  2  X  0.045  g'  °f  hydrogen  and 
0.715^-  of  oxygen,  and  accordingly  weighs  0.805^-. 
Knowing  this,  we  can  write  the  proportions : 
0.09          x 
0.805  ""  100 
0.715         y 


0.805 


Combining  and  Elemental  Weights  125 

where  x  and  y  represent  the  percentages  of  hydro- 
gen and  oxygen,  respectively.  Solving  the  propor- 
tions, we  have : 

x  —  11.19 

y  =  88.81 

^.  It  stands  for  a  definite  volume  of  a  gaseous 
compound. 

138.  Determination  of  the  Formula  of  a  Com- 
pound which  can  be  Vaporized.  It  is  customary  to 
express  the  results  of  the  analysis  of  a  compound  in 
parts  per  hundred.  If  the  percentage  composition 
of  a  compound  and  the  weight  of  a  liter  of  it  in  the 
gaseous  state  is  known,  its  formula  may  be  estab- 
lished as  illustrated  in  what  follows. 

The  weight  of  a  liter  of  water  vapor  is  0.805  *'<> 
and  water  contains  11.19  Per  cent  of  hydrogen  and 
88. 8 1  per  cent  of  oxygen. 

From  the  proportion : 

11.19          x 
100        0.805' 
x    =    0.09, 

it  follows  that  a  liter  of  water  vapor  must  contain 
0.09 -?"•  of  hydrogen.  But  0.09  =  2  X  0.045.  Hence 
H2  must  occur  in  the  formula. 

Likewise  from  the  proportion  : 

88.81  _       y 
100         0.805' 
7  =  0.715, 

and  0.71 5  *"•  is  therefore  the  weight  of  the  oxygen  in 
one  liter  of  water  vapor,  and  as  0.715  is  the  elemen- 
tal weight  of  oxygen,  O  must  occur  in  the  formula. 


126       -  Elementary  Chemistry 

The  sum  of  0.09  and  0715  is  0.805,  and  the  for- 
mula of  water  vapor  must  therefore  be  H2O. 

139.  Determination  of  the  Formula  of  an  Invola- 
tile  Compound.  Many  compounds  are  so  involatile 
that  the  weight  of  a  liter  of  their  vapor  cannot  be 
determined.  Still  formulas  may  be  established  for 
them  from  their  percentage  composition,  although 
they  are  necessarily  somewhat  ambiguous.  Evi- 
dently the  ratio  of  the  numbers  expressing  the  per- 
centage composition  must  also  be  the  ratio  of  the 
elemental  or  combining  weights,  multiplied  by  the 
integers  i,  2,  3,  4,  and  so  on,  as  the  case  may  be. 

Suppose,  for  example,  that  water  could  not  be 
vaporized.  We  know  that  it  contains  11.19  Per  cent 
of  hydrogen  and  88. 8 1  per  cent  of  oxygen.  Now 
the  ratio  of  1 1.19  to  0.045  is  the  same  as  the  ratio  of 
248.4  to  i  ;  and  88.8 1  :  0.7 1 5  : :  1 24.2  :  i .  But  the  ratio 
of  248.4  to  124.2  is  the  same  as  2  to  i.  Water  has 
therefore  the  formula,  H2O.  It  is  indeed  left  unde- 
cided as  to  whether  the  formula  might  not  also  be 
H4O2,  H6O3,  and  so  on,  as  the  subscripts  of  these 
formulas  are  also  in  the  ratio  of  2  :  i.  It  is  cus- 
tomary, however,  to  choose  the  simplest  ratio. 

The  same  result  may  be  arrived  at  by  the  use  of 
combining  weights.  Thus,  in  the  case  of  water,  the 
ratio  of  the  percentage  of  hydrogen  to  its  combin- 
ing weight  is  11.19:  i,  and  that  of  the  percentage 
of  oxygen  to  its  combining  weight,  88. 8 1  :  16  (or, 
more  accurately,  88. 8 1  :  15.88),  which  is  the  same 
as  5.59  :  i.  But  11.19  *s  twice  5.59;  hence  the  for- 
mula is  H2O. 

The  formula  of  a  compound  may  thus  be  found 
by  dividing  the  percentage  of  each  element  by  its 


Combining  and  Elemental  Weights  12^ 

elemental  or  combining  weight,  and  reducing  the 
quotients  which  denote  the  number  of  times  a 
symbol  occurs  in  a  formula  to  the  simplest  ratio. 
It  may  happen  that  this  ratio  is  not  found  to  con- 
sist of  whole  numbers.  Thus,  perhaps  i  :  2.03  :  3.98 
may  have  been  found.  In  such  cases  the  slightly 
differing  integral  numbers  1:2:4  may  without 
question  be  substituted,  for  the  numbers  express- 
ing the  percentages  are  obtained  by  experiment 
and  hence  are  liable  to  error.  It  has  ever  been 
found  that  the  more  accurate  the  analysis,  the  less 
the  numbers  in  the  ratio  differ  from  integers. 

140.  Formula  Weights.     The  formula  weight 
of  a  compound  is  the  weight  of  it  in  grams  numer- 
ically equal  to  the  sum  of  the  combining  weights 
of  the  elements  occurring  in   the   formula.     The 
formula  weight  of  nitric  acid,  HNO3,  is: 

i  +  14 +  (3  X  i6)  =  63* 

The  conception  of  formula  weights  leads  to  a 
new  wording  of  the  Law  of  the  Conservation  of 
Matter: 

In  any  cJicmical  reaction  the  sum  of  the  formula 
weights  of  the  factors  must  equal  the  sum  of  the  formula 
weights  of  the  products. 

141.  Chemical  Equations.     Chemical  equations 
gain  much  in   simplicity  by  the  use  of  formulas. 
The  equation  representing  the  burning  of  hydro- 
gen is: 

2H2  +02  ->2H20 

The  numerical  coefficient  denotes  that  the  whole 
formula  is  to  be  multiplied  by  it  just  as  in  algebra. 
Thus,  2  H2O  means  that  there  are  2X2  hydrogen 


128  Elementary  Chemistry 

symbols  and  2  X  i  oxygen  symbols.  The  combus- 
tion of  carbon  in  a  limited  and  in  an  abundant 
supply  of  oxygen  is  shown  thus  : 


C  +  O2  -^    CO2 

The  combustion  of  (a)  methane,  (b)  ethylene,  and 
(V)  acetylene  is  represented  by  these  equations  : 

(a)  CH4  +  2O2-^     CO2  +  2H2O 

(b)  C2H4  +  302->2C02  +  2H20 

(c)  2C2H2+  5O2^4CO2  +  2H2O 

That  these  equations  are  in  accordance  with  the 
Law  of  the  Conservation  of  Matter  is  proved  by 
adding  the  formula  weights  of  the  factors  and  of 
the  products  and  comparing  the  two  sums  for 
equality.  Thus,  in  the  equation  for  the  combustion 
of  acetylene,  if  we  write  the  formula  weights  under 
the  formulas  and  multiply  them  by  the  number  of 
times  they  occur,  we  have  : 

2C2H2  +  $02      ->  4C02  +  2H20 

2x26+5x32  =  4X44  +  2X18 

52       +    1  60      =     176      +     36 

212  212 

142.  Balancing  Equations.  When  the  factors 
and  products  of  a  chemical  reaction  are  known  and 
their  formulas  are  written  in  the  form  of  an  equa- 
tion, it  is  very  seldom  that  the  sums  of  the  formula 
weights  of  factors  and  of  products  are  the  same.  It 
is  then  necessary  to  increase  the  number  of  some 
or  all  of  the  formulas  until  the  formula  weights  of 
both  factors  and  products  are  the  same.  Among 
the  simplest  of  chemical  reactions  are  those  in 


Combining  and  Elemental  Weights  129 

which  a  substance  containing  carbon  and  hydro- 
gen, or  carbon,  hydrogen,  and  oxygen  is  burned ; 
the  sole  products  of  such  combustions  are  carbon 
dioxid  and  water.  We  shall  accordingly  make  use 
of  these  ''combustion  equations"  in  explaining  the 
balancing  of  equations. 

/.     To  illustrate,  suppose  we  have  burned  ethy- 
lene,  C2H4,  and  have  found  that  the  sole  products 
are  water,  H2O,  and  carbon  dioxid,  CO2.     We  con- 
nect the  factors  with  the  plus  sign  as  also  the  prod- 
ucts, and  write  under  the  formulas  their  weights: 
C2H4  +02  -*C02  +  H20 
28+32          44+18 
60  62 

The  sums  of  the  formula  weights  of  factors  and 
products  are  seen  to  be  unequal ;  the  equation  is 
not  balanced.  As  the  carbon  symbol  occurs  twice 
in  the  factors  it  must  also  occur  twice  in  the  prod- 
ucts, for  it  stands  for  a  definite  -weight  of  carbon. 
Likewise  the  hydrogen  symbol  occurs  four  times  in 
the  factors  and  but  twice  in  the  products.  Making 
the  changes  thus  required,  we  have : 

C2H4  +02  -^2H20  +  2C02 

28      +32         2  X  18  +  2  X  44 
60  1 24 

But  this  makes  the  oxygen  symbol  occur  six  times 
in  the  products,  while  it  occurs   but  twice  in  the 
factors.     We  therefore  increase  the  number  of  oxy- 
gen symbols  in  the  factors  to  six  and  then  have : 
C2H4  +  3O2  ->2H2O  +  2  CO2 
"  28  +  3  X  32          ~36  +  88 
i 24  i 24 


10 


130  Elementary  Chemistry 

As  the  sum  of  the  formula  weights  is  now  the  same 
on  both  sides,  we  write  the  balanced  equation : 

C2H4  +  302  -^2H20  +  2C02 
2.     As  a  second  example  take  the  combustion  of 
alcohol,  C2H6O,  the  products  of  which  are  water 
and  carbon  dioxid  as  before.     We  first  write : 

C2H60  +  02  _»H20+C02 

46  +  32  18+44 

78  62 

This  does  not  balance,  and  so  we  double  the  num- 
ber of  carbon  symbols  and  treble  the  number  of 
hydrogen  symbols  in  the  products,  thus  obtaining : 

C2H60  +  02  -»3H26+2C02 

46  +  32        3  X  18  +  2  X  44 
78  142 

This  also  does  not  balance,  and  we  see  that  while 
there  are  seven  oxygen  symbols  in  the  products, 
there  are  but  three  (one  is  in  the  alcohol  formula) 
in  the  factors.  By  trebling  the  oxygen  formula, 
however,  we  arrive  at  the  balanced  equation : 

C2H60  +  302  X  3H?0  +  2C02 
46  +  3  X  32          54+88 
142  142 

j.  Let  us  consider  for  a  third  example  the  com- 
bustion of  glycerin,  C3H8O3,  the  products  of  which 
are,  as  in  the  two  previous  examples,  water  and  car- 
bon dioxid.  We  first  have  : 

C3H803  +  02  -^4H20  +  3C02 
92  +  32        4  X  18  +  3  X  44 
i 24  204 

There  are  now  ten  oxygen  symbols  in  the  prod- 
ucts and  five  in  the  factors.  Subtracting  the  three 


Combining  and  Elemental  Weights  131 

oxygen  symbols  contained  in  the  glycerin  formula, 
we  have  seven  left.  Evidently  then  we  shall  have 
to  multiply  the  O2  by  7/2  =  3^  in  order  to  balance 
the  equation.  But  for  reasons  that  will  be  stated 
later  it  is  not  permissible  to  use  fractional  coeffi- 
cients. To  avoid  this  we  multiply  the  whole  equa- 
tion by  two,  thus  getting  the  balanced  equation : 
2C3H8O,  +  ;O2  — >  8H2O  +  6CO2 

2  X  92  +  7  X  32       8  X  18  +  6  X  44 
408  408 

143.  The  General  Procedure.  The  foregoing 
illustrations  will  probably  make  clear  the  mechan- 
ism of  balancing  "  combustion  equations."  The 
formula  of  the  combustible  and  of  oxygen  are  con- 
nected with  the  plus  sign  and  an  arrow  is  added  to 
show  that  these  factors  are  converted  into  the  prod- 
ucts, carbon  dioxid,  CO2,  and  water,  H2O.  The  sole 
products  of  the  combustion  of  any  compound  con- 
taining carbon  and  hydrogen,  or  carbon,  hydrogen, 
and  oxygen,  are  always  carbon  dioxid  and  water. 
Coefficients  numerically  equal  to  the  subscripts  of 
the  carbon  and  hydrogen  symbols  in  the  formula  of 
the  combustible  are  prefixed  to  the  formulas  of  the 
carbon  dioxid  and  the  water.  If,  however,  the  sub- 
script of  H  in  the  combustible's  formula  is  an  odd 
number,  all  the  formulas  except  that  of  O2  (which 
is  left  to  the  last)  are  doubled.  When  by  this  pro- 
cedure the  same  number  of  carbon  and  of  hydrogen 
symbols  are  obtained  in  both  members,  the  number 
of  oxygen  symbols  in  the  products  is  counted  up, 
and  from  this  is  subtracted  the  number  of  oxygen 
symbols  in  the  formula  of  the  combustible,  or  the 
formula  doubled,  as  the  case  may  be.  Half  of  this 


132  Elementary  Chemistry 

difference  gives  the  coefficient  of  the  oxygen  for- 
mula. If,  however,  this  difference  is  an  odd  num- 
ber, half  of  it  will  be  a  mixed  number,  and  as  the 
coefficients  must  be  integral,  all  four  formulas  must 
be  doubled. 

These  two  points  should  always  be  borne  in  mind : 
(/)  The  coefficients  must  be  integral.  (2)  TJie  sum  of 
the  formula  weights  of  tlie  factors  must  equal  that  of  the 
products,  or,  in  other  words,  the  products  must  contain 
the  same  number  of  each  symbol  as  tJie  factors. 

144.  Volumes.  The  formula  of  a  gaseous  or 
volatile  compound  stands  for  a  definite  volume  of 
it, —  for  one  liter,  when  the  system  of  elemental 
weights  is  used,  and  for  22. 2  L  when  the  system  of 
combining  weights  is  adopted.  If  the  elemental 
weights  of  the  elements  are  added  together  with 
due  allowance  for  the  number  of  times  a  symbol 
occurs  in  a  formula,  the  weight  of  a  liter  of  the 
gaseous  compound  under  standard  conditions  is 
obtained.  Thus,  from  the  formula  of  alcohol, 
C2H6O,  a  liter  of  alcohol  vapor  weighs 

(2  X  0.536)  +  (6  x  0.045)  +  0.715  =  2.057^- 

The  equation  for  the  combustion  of  alcohol 
(§  142)  may  be  read  : 

One  liter  of  alcohol  vapor,  weighing  2.057^-,  com- 
bines with  3 l-  of  oxygen,  weighing  3  X  1 43  =  4.29  *-, 
to  give  37-  of  water  vapor,  weighing  3  X  0.805^-,  and 
2L  of  carbon  dioxid,  weighing  2  X  1.966^-. 

NOTE.  Combustion  equations  only  have  thus  far  been  consid- 
ered. These  are  not  only  numerous  and  important,  but  are  also 
relatively  simple  to  balance.  Later  we  shall  consider  the  balancing 
of  equations  representing  reactions  other  than  those  of  combustion. 
The  general  procedure  is  similar ;  the  same  principles  hold  good. 


Combining  and  Elemental  Weights  133 

145.  Combustion  of  Organic  Compounds  Con- 
taining Nitrogen.   When  any  compound  containing 
carbon  and  nitrogen  is  burned,  the  products  of  the 
combustion  are  carbon  dioxid  and  free  nitrogen,  N2. 
If  hydrogen  is  present  in  the  compound,  it  burns 
to  water.     The  products  of  the  combustion  of  com- 
pounds containing  carbon,  hydrogen,  oxygen,  and 
nitrogen  are  then  always  carbon  dioxid,  water,  and 
free  nitrogen.     For  example,  the  balanced  equation 
for  the  combustion  of  nitrobenzene,  C6H5NO2,  is: 

4C6HSNO2  +  250,  -^24CO2  +  ioH2O  +  2N2 

146.  Usefulness  of  Chemical  Equations.    Equa- 
tions not  only  give  a  simple  representation  of  a 
chemical  reaction,  but  are   also  of  great  value  in 
ascertaining  the  mass  relationships  of  the  reacting 
substances.     Suppose  we  wish  to  know  how  much 
carbon  dioxid  and  water  can  be  obtained  from  the 
total   combustion   of   50^-   of   turpentine,   C10H16. 
The  combustion  equation  is : 

C10H16  +  i4O2  -»  ioCO2  +  8H2O 
136  +  448  440  +  144 

584  584 

Hence,  1 36  parts  by  weight  of  turpentine  combine 
with  448  parts  of  oxygen  to  give  440  parts  of  car- 
bon dioxid  and  144  parts  of  water.  Then  50  *"•  of 
turpentine  unites  with  50/136  X  448  =  164.7 8'  °f 
oxygen  to  yield  50/136  X  440  =  161. 8  ^-  of  carbon 
dioxid  and  50/136  X  144=52.9^-  of  water.  The 
balanced  equation  shows  what  are  the  relative 
proportions  by  weight  in  terms  of  the  combining 
weights  or  formula  weights  according  to  which  the 
reaction  occurs.  As  these  weights  are  ratios,  it  is  a 

•  •• 

A 
or  THE 

lf*.lll/r**«*f«r*vs 


134  Elementary  Chemistry 


problem  of  ratio  and  proportion  to  convert  them 
into  other  sets  of  weights. 

ANALYSIS  OF  ORGANIC  COMPOUNDS.  Many  of  the 
most  familiar  substances  contain  carbon  united  with 
hydrogen  (the  hydrocarbons),  or  with  hydrogen  and 
oxygen  (alcohols,  organic  acids,  sugars,  starch,  cellulose, 
etc.),  or  with  hydrogen,  oxygen,  and  nitrogen  (alkaloids, 
anilin  dyes,  etc.).  "it  is  possible  only  in  extremely  few 
cases  to  separate  the  carbon,  oxygen,  and  hydrogen  in 
the  free  state.  Nitrogen,  however,  is  obtained  free 
when  compounds  containing  it  are  burned.  The  prod- 
ucts of  the  combustion  of  these  organic  compounds 
are  always  water,  carbon  dioxid,  and  nitrogen,  and  the 
method  of  analyzing  them  is  based),  upon  this  fact.  A 
definite  weight  of  the  substance  is  burned  in  oxygen 
or  is  heated  with  some  oxidizing  agent,  as  potassium 
chlorate  or  copper  oxid,  and  the  products  of  the  com- 
bustion passed  through  tubes  containing  some  deliques- 
cent substance,  as  calcium  chlorid  or  sulf  uric  acid,  which 
retains  the  water,  and  then' through  caustic  potash  solu- 
tion, which  absorbs  the  carbon  dioxid.  The  nitrogen 
is  collected  in  a  graduated  tube  over  water  or  mercury. 

The  increase  in  the  weights  of  the  tubes  containing 
the  deliquescent  substance  and  the  potash  solution 
gives  the  weights  of  the  water  and  the  carbon  dioxid, 
respectively,  produced  by  the  combustion.  As  carbon 
dioxid  contains  12/44  =  3/11  =  27.27  per  cent  of  its 
weight  of  carbon,  and  water  2/18  =  1/9  =  11.19  Per 
cent  of  its  weight  of  hydrogen,  the  weights  of  the  car- 
bon and  the  hydrogen  contained  in  the  compound  may 
easily  be  found.  The  sum  of  the  weights  of  the  carbon 
and  the  hydrogen  thus  calculated,  subtracted  from  the 
weight  of  the  combustible,  gives  the  weight  of  the 
other  elements  present.  As  we  shall  consider  com- 
pounds containing  only  carbon,  hydrogen,  oxygen,  and 
nitrogen,  and  as  it  has  been  found  best  to  make  a 
separate  determination  of  nitrogen,  the  above  weight 
obtained  by  difference  is  counted  as  oxygen. 

The  results  of  an  analysis -are,  almost  without  excep- 
tion, expressed  in  per  cents.  The  calculation  of  the 
percentage  composition  is  explained  in  §§  138  and  139. 


Combining  and  Elemental  Weights  135 

Problems 

/.  If  the  formula  of  oxygen  is  O2,  what  do  22.2^-  of  the  gas 
weigh  ? 

2.  If  22.2^-  of  cyanogen  contain  24^-  of  carbon  and  28 <r-  of 
nitrogen,  what  is  its  formula  ? 

j>.  One  liter  of  hydrazin  weighs  1.43^-  and  contains  o.  18&-  of 
hydrogen.  What  is  its  formula  ? 

4.  Find  the  percentage  composition  to  two  decimals  of  am- 
monia,   methane,    carbon    dioxid,   alcohol    (C2H6O),   and    anilin 
(C6H7N). 

5.  There  is  a  hydrocarbon  called  ethane,  the  weight  of  i '• 
of  which  is  1.346^-  and  which  contains  80  per  cent  of  carbon. 
What  is  its  formula  ? 

6.  Find  the  formula  of  hydrazoic  acid,  knowing  that  it  con- 
tains 97.69  per  cent  of  nitrogen  and  2.31  per  cent  of  hydrogen,  and 
that  one  liter  weighs  1.92^"-. 

7.  If  the  elemental  weight  of  sulfur  is  1.43  and  if  i  /•  of  its 
gas  weighs  2.86<5r-,  what  is  its  formula  ? 

8.  Hydrogen  dioxid  contains  94.12  per  cent  of  oxygen.     Cal- 
culate its  formula. 

9.  The  percentage  composition  of  nitric  acid  is  as  follows  : 
H  =  1.59$  ;  O  =  76.19$  ;  N  =  22.22$.     Calculate  its  formula. 

10.  What  are  the  formula  weights  of  the  following  substances  : 
Carbon    dioxid,   water,    acetylene,    ethylene,    methane,    alcohol 
(C2H6O),  glycerin  (C3HbO3),  acetic  acid  (C2H4O2),  benzene  (C6H6), 
turpentine  (Ci0H16),  sugar  (daHaaOn),  camphor  (C10H16O),  starch 
(C6H1005). 

11.  When  any  compound  of  carbon  and  hydrogen  (hydrocar- 
bon), or  of  carbon,  hydrogen,  and  oxygen,  is  burned  in  a  plenti- 
ful supply  of  oxygen,  the  sole  products  are  water  and  carbon 
dioxid.     Complete  and  balance  the  following  equations  : 

(1)  C2H402         +     02-»? 
(acetic  acid} 

(2)  C6HB  +     02   — »? 
(benzene} 

(3)  CH.,0  +     02-^? 
(methyl  alcohol} 

(4)  C6H60          +     02  ->? 
(carbolic  acid) 

(5)  C10H16         +     02->? 
(turpentine) 


136  Elementary  Chemistry 

(6)  C10H1G0 
{f amp  nor) 

(7)  C^H^O^ 

(sugar) 

(8)  C6H1005 

(starch} 

12.     Complete  and  balance,  bearing  in  mind  that  nitrogen  will 
be  separated  out  in  the  free  state  and  will  have  the  formula,  N2  : 


(I) 

(2) 

(3) 
(4) 
(5) 

C6H7N 
(anilin}    , 
C«HN 
(pyridine} 
C17H19N03     H 
(morphine) 
C2tH22N202    H 
(strychnine} 
C17H21N04      H 

h     02 
h     02 

r       0, 

-    o2 

(cocaine} 

fj.  How  many  grams  of  oxygen  are  required  to  burn  50  Sr- 
of  methane,  and  how  many  grams  of  water  and  carbon  dioxid 
are  produced? 

Solution  :     The  equation  is  : 

CH4  +  202  =  C02  +  2H20 
16    +    64  44     +     36 

80  80 

64/16  X  50  =  200,  the  number  of  grams  of  oxygen  required. 
44/16  X  50=  137.5,  the  number  of  grams   of  carbon  dioxid 
produced. 

36/16  X  50  =  112.5,  the  number  of  grams  of  water  produced. 

14.  88  &•  of  carbon  dioxid  were  obtained  from  the  combustion 
of  acetylene.  How  much  acetylene  was  burned  and  how  much 
oxygen  did  it  require  ? 

Solution :     The  equation  is  : 

2C,H2  +  50,  =  4CO2  +  2^30 
52       +   160  176     +     36 

212  212 

52/176  X  88  =  26,  the  number  of  grams  of  acetylene. 
160/176  X  88  =  80,  the  number  of  grams  of  oxygen. 

75.  How  much  oxygen  does  it  take  to  just  burn  156  £•  of  ben- 
zene, C6H6,  and  how  much  water  and  carbon  dioxid  are  produced? 


Combining  and  Elemental  Weights  137 

16.  22  &•  of  carbon  dioxid  were  obtained  by  the  burning  of 
alcohol,  C2H6O.  How  much  alcohol  and  oxygen  were  required? 

//.  How  much  starch,  CGH10O5,  has  to  be  burned  to  give 
72  <?"•  of  water  ? 

18.  How  many  grams  of  nitrogen  and  of  water  are  obtained 
from  the  combustion  of  ioo<?"-  of  anilin,  CGH7N  ? 

ig.  Turpentine  is  a  hydrocarbon.  o.SSo^-  of  CO2  and  0.288 &• 
of  H2O  were  obtained  when  0.272  <£"•  of  it  were  burned.  What  is 
its  percentage  composition  ? 

Solution:  o.SSo<f-  of  carbon  dioxid  contains  0.880  X  12/44  = 
0.240^"-  of  carbon,  and  o.288<?"-  of  water  contains  0.288  X  1/9  = 
0.032  £•  of  hydrogen.  Then  0.272  :  0.240  :  :  100  :  x,  whence  x  = 
88.24,  the  percentage  of  carbon;  and  0.272  :  0.032  :  :  100  :  y,  whence 
y  =  11.76,  the  percentage  of  hydrogen. 

20.  Camphor  contains  carbon,  hydrogen,  and  oxygen.    o.6o8,f- 
were  burned  and  yielded  i.76o<T-  of  CO2  and  o.576<?"-  of  H,O. 
Find  its  percentage  composition. 

21.  0.4536^-  of  starch  (which  contains  carbon,  hydrogen,  and 
oxygen)  yielded  when  burned  0.7392.:?'-  of  CO,   and  0.2521^"-  of 
H2O.     What  is  its  percentage  composition? 

22.  If  a  liter  of  turpentine  vapor  weighs  6.o8<T',  find  its  for- 
mula from  the  percentage  composition  calculated  in  Problem  19. 

23.  Find  the  formula  of  camphor,  knowing  its  percentage 
composition  (Problem  20)  and  that  22.2  t-  of  its  vapor  weigh  i52<f- 

24.  What  is  the  simplest  formula  for  a  compound  containing 
72.44  per  cent  of  carbon,  6.09  per  cent  of  hydrogen,  and  21.47  per 
cent  of  oxygen  ? 

25.  What  is  the  volume  at  20°  and  746^^-  of  the  nitrogen 
given   off  in   the  combustion  of   i6.84<?"-   of  a  compound  whose 


CHAPTER  XIII 

THE  ATOMIC  THEORY— VALENCE 

147.  The  Constitution  of  Matter.    Two  hypoth- 
eses as  to  the  constitution  of  matter  merit  attention 
here: 

/.  Matter  may  be  perfectly  continuous  in  struc- 
ture, a  vacuum  or  empty  portion  of  space  being 
regarded  as  impossible. 

2.  Matter  may  consist  of  separate  and  distinct 
parts  more  or  less  isolated  in  space. 

Opinions  differ  as  to  which  of  these  two  hypoth- 
eses represents  the  facts  the  better,  but  inasmuch 
as  the  second  gives  a  simple  explanation  of  the 
Laws  of  Chemical  Combination,  it  has  become  inter- 
woven with  the  chemistry  of  the  nineteenth  cen- 
tury ;  so  much  so,  indeed,  that  the  theory  is  often 
considered  by  some  as  of  more  importance  than 
the  facts  which  it  is  supposed  to  account  for.  But 
it  should  ever  be  kept  in  mind  that  a  hypothesis  or 
theory  is  necessarily  temporary  and  is  subordinate 
to  the  facts. 

148.  Atoms  and  Molecules  ;  Electrons.     Matter 
then  is  supposed  to  consist  of  a  multitude  of  minute 
particles  of  definite  mass  more  or  less  separated  in 
space.     Suppose  a  piece  of  paper  to  be  torn  up  into 
as  small  bits  as  possible,  and  let  these  bits  be  cut 
up  into  as  many  parts  as  the  finest  razors  will  per- 
mit ;  the  paper  still  remains  paper.     Let  us  imagine 
the  division  to  be  carried  further  and  further.     We 


The  Atomic  Theory  —  Valence  139 

shall  arrive  finally  at  such  a  small  piece  of  paper 
that  it  cannot  be  divided  again  without  its  ceasing 
to  be  paper.  We  then  say  that  we  have  to  do  with 
a  molecule  of  paper. 

Generally  speaking,  a  molecule  may  be  denned 
as  the  smallest  part  of  matter  that  can  exist  in  a  free 
state  and  retain  the  properties  of  the  substance. 

But  the  molecule  of  paper  can  be  divided  further 
into  still  smaller  parts,  which  have  been  given  the 
name  of  atoms.  The  atoms  in  this  case  are,  how- 
ever, not  paper,  but  the  elements  composing  paper, 
namely,  carbon,  hydrogen,  and  oxygen. 

Until  recently  it  has  been  supposed  that  atoms 
are  the  smallest  parts  into  which  elements  can  be  divided. 
But  it  is  now  known  that  there  exist  still  smaller 
particles  which  are  called  electrons.  Their  existence 
has  been  brought  to  light  by  electrical  means,  and 
does  not  affect  essentially  the  views  on  atoms  which 
chemists  have  held. 

A  few  elements,  as  mercury  and  some  other  met- 
als, seem  to  have  their  atoms  and  molecules  iden- 
tical ;  but,  as  a  rule,  atoms  of  the  same  kind  unite  to 
form  molecules.  Thus,  the  molecules  of  the  ele- 
mentary gases  we  have  studied  consist  of  two  atoms 
each.  This  is  in  accordance  with  the  fact  that  the 
weight  of  a  liter  of  any  of  these  gaseous  elements 
is  double  its  elemental  weight.  As  we  shall  see 
later,  the  elemental  and  combining  weights  are  pro- 
portional to  the  weights  of  the  atoms  themselves. 

There  are  as  many  different  kinds  of  atoms  as 
there  are  of  elements,  but  the  ntimber  of  different 
kinds  of  molecules  is  boundless.  It  has  been  calcu- 
lated that,  if  a  single  drop  of  water  were  magnified 


140  Elementary  Chemistry 

to  the  size  of  the  earth,  the  molecules  would  be  a 
little  larger  than  base-balls.  This  may  give  some 
idea  of  the  minuteness  of  atoms  and  molecules  and  of 
the  enormous  number  of  them  contained  in  even  the 
smallest  portion  of  matter  we  are  able  to  perceive 
with  the  aid  of  our  most  powerful  microscopes. 

HISTORICAL  NOTE.  The  conception  of  matter  as 
being  made  up  of  atoms  endowed  with  certain  prop- 
erties or  qualities  is  quite  ancient.  It  was  first  pro- 
pounded by  the  Greek  philosophers,  Leucippus  and 
Democritus,  in  the  fifth  century,  B.  C.  Their  concep- 
tion of  atoms  was  a  mere  speculation,  however,  and  it 
was  not  until  the  beginning  of  the  nineteenth  century 
that  it  was  revived  by  John  Dalton  to  account  for  the 
Laws  of  Definite  and  Multiple  Proportions. 

149.  The  Atomic  Theory.  The  usefulness  of 
the  hypothesis  of  atoms  lies  in  the  simple  account 
it  renders  of  the  Laws  of  Definite  and  Multiple  Pro- 
portions, and  the  hypothesis  has  consequently  been 
elaborated  into  a  theory.  We  have  learned  that 
when  elements  combine  with  one  another  the  union 
takes  place  according  to  fixed  proportions,  and  that 
the  analysis  of  any  sample  of  a  definite  chemical 
compound  always  gives  the  same  results.  Now  we 
are  quite  free  in  our  choice  of  units  to  express  the 
combining  proportions  of  the  elements;  we  may 
use  grams,  tons,  pounds,  or  any  other  unit  of  mass 
we  see  fit.  We  have  already  employed  two  ways 
of  expressing  the  ratio  of  the  quantities  of  elements 
in  compounds.  In  one  we  took  the  smallest  weight 
in  grams  contained  in  a  liter  of  any  of  their  gaseous 
compounds,  and  called  these  weights  the  elemental 
weights.  In  the  other  we  chose  the  parts  by  weight 
that  express  the  ratios  when  referred  to  hydrogen 


The  Atomic  Theory  —  Valence  141 

as  unity,  and  called  these  weights  the  combining 
weights.  But  we  might  also  adopt  numbers  meant 
to  represent  the  weights  of  the  atoms  themselves. 
If  the  mass  of  a  hydrogen  atom  be  taken  as  unity, 
the  masses  of  the  carbon,  nitrogen,  and  oxygen 
atoms  are  12,  14,  and  16  times  the  unit  mass,  respect- 
ively. Our  ignorance  of  the  actual  weights  of  the 
atoms  is  no  hindrance,  for  these  sets  of  numbers  are 
ratios  and  hence  independent  of  the  unit  we  adopt. 

The  relationships  which  have  been  established 
for  the  combining  weights  can  then  be  expressed  in 
terms  of  atomic  weights.  The  molecular  weights  of 
the  elements  will  depend  upon  the  number  of  atoms 
which  compose  their  molecules.  In  the  case  of  hy- 
drogen, nitrogen,  and  oxygen  the  molecular  weights 
are  double  the  atomic  weights.  As  we  do  not  know 
how  many  atoms  compose  the  carbon  molecule,  we 
are  forced  to  assume  that  its  molecular  and  atomic 
weights  are  the  same.  The  molecular  weight  of  a 
compound  is  equal  to  the  sum  of  the  atomic  weights 
of  the  elements  composing  it.  Thus,  the  molecular 
weight  of  water  is  1 8  ;  that  of  carbon  dioxid,  44. 

150.  Laws  Accounted  for  by  This  Theory.  If 
then  we  assume  that  on  an  average  the  atoms  of  the 
same  element  have  equal  masses,  we  can  readily 
account  for  the  Laws  of  Definite  and  Multiple  Pro- 
portions. Thus,  one'  or  more  atoms  of  one  element 
may  combine  with  one  or  more  atoms  of  another 
element  to  form  a  molecule  of  a  compound  con- 
taining both  elements.  For  example,  one  atom  of 
carbon  combines  with  one  atom  of  oxygen  to  pro- 
duce one  molecule  of  carbon  monoxid,  CO.  Also, 
one  atom  of  carbon  combines  with  two  atoms  of 


142  Elementary  Chemistry 

oxygen  to  form  one  molecule  of  carbon  dioxid, 
CO2.  Now,  since  atoms  are  indivisible,  one  carbon 
atom  cannot  combine  with,  say,  one  and  a  half  or  one 
and  a  fifth,  of  an  oxygen  atom,  for  fractional  atoms 
are  supposed  not  to  exist.  Combination  must  take 
place  between  whole  atoms,  and  when  several  com- 
pounds may  be  prepared  from  two  or  more  atoms 
of  different  elements,  only  integers  can  represent 
the  numbers  of  atoms.  The  Laws  of  Definite  and 
Multiple  Proportions  follow  necessarily.  Fractions 
of  atoms  cannot  exist ;  hence  combinations  between 
atoms  must  be  expressible  by  integers. 

The  atomic  theory  supposes  then  that  what  we 
observe  in  any  chemical  action  is  the  result  of  a 
vast  number  of  similar  actions  occurring  between 
the  atoms. 

The  atomic  theory  will  be  applied  from  now  on. 
Instead  of  speaking  of  elemental  or  combining 
weights,  we  shall  say  atomic  and  molecular  weights. 
The  symbols  and  formulas  shall  stand  for  the  vol- 
umes and  weights  of  atoms  and  molecules.  Thus, 
the  formula  for  alcohol,  C2H6O,  stands  for  the  vol- 
ume which  the  alcohol  molecule  in  the  gaseous 
state  occupies,  and  shows  that  the  molecule  consists 
of  two  atoms  of  carbon,  six  of  hydrogen,  and  one  of 
oxygen.  It  has  been  more  or  less  roughly  esti- 
mated that  a  liter  of  any  elementary  gas  contains 
about  i  ,000,000,000,000,000,000,000,000  molecules,  so 
that  the  weight  of  one  molecule  of  hydrogen  is 

-~  grams,  an  extremely  small  number.     It  is  of 

no  particular  advantage,  however,  to  know  the  exact 
weight  of  an  atom  or  a  molecule. 


The  Atomic  Theory  —  Valence  143 

VALENCY 

151.  Equations  in  Terms  of  Molecules  and 
Atoms.     Let  us  again  consider  the  combustion  of 
alcohol.     We  know  that  its  formula  in  the  gaseous 
state   is  C2H6O,  so  that  in  terms   of  the  Atomic 
Theory  a  molecule  of  alcohol  is  made  up  of  two 
atoms  of  carbon,  six  of  hydrogen,  and  one  of  oxy- 
gen.   We  also  know  how  many  atoms  are  contained 
in  a  molecule  of  oxygen,  O2,  and  in  a  molecule  of 
water,  H2O,  and  carbon  dioxid,  CO2.     Now  atoms 
are  indestructible ;  hence  the  number  of  atoms  in 
the  factors  of  a  reaction  must  equal  the  number  of 
atoms   in  the   products.     In   order  to   balance   an 
equation  we   accordingly  proceed   as  set  forth  on 
page  131,  bearing  in  mind  that  if  the  same  number 
of  atoms  of  a  kind  are  in  both  members  of  the 
equation,  it  is  balanced.     The  sum  of  the  molecular 
or   atomic  weights   of   the   factors    of   a   chemical 
reaction  is  then  equal  to  the  sum  of  the  molecular 
or  atomic  weights  of  the  products. 

152.  Value  of  Chemical  Equations.     Equations 
do  not  tell  everything  about  a  reaction;  they  are 
usually  but  ideal  or  rather  perhaps  average  expres- 
sions of  the  facts.    Variations  in  temperature,  pres- 
sure, and  strength  of  reagents  cause  considerable 
variations  in  reactions.     A  reaction  taking  place 
according  to  one  equation  under  certain  conditions 
may  proceed  according  to  quite  a  different  equation 
when  the  conditions  are  changed.     Equations  tell 
the  quantitative  facts  under  special  qualitative  con- 
ditions, and  attempt  nothing  more.     They  are  of 
value,  however,  but   should  be   used  with  proper 
limitations. 


144  Elementary  Chemistry 

153.  Valency.  We  have  seen  that  one  volume 
of  oxygen  combines  with  two  volumes  of  hydrogen 
to  produce  two  volumes  of  water  vapor;  that  one 
volume  of  nitrogen  combines  with  three  volumes 
of  hydrogen  to  produce  two  volumes  of  ammonia, 
and  later  we  shall  learn  that  one  volume  of  chlorin 
combines  with  one  volume  of  hydrogen  to  yield 
two  volumes  of  hydrogen  chlorid.  From  these 
instances  it  is  apparent  that  different  elements  have 
different  capacities  for  combination,  and  we  shall 
find  that  this  is  generally  true.  This  power  of 
combination  is  characteristic  of  an  element,  and  is 
called  its  valency. 

A  consideration  of  the  following  formulas  may 
serve  to  illustrate  valency  : 

HC1        H2O         H3N         H4C 

It  is  seen  that  carbon,  for  instance,  unites  with 
four  times  as  much  hydrogen  as  does  chlorin. 

Hydrogen  is  assumed  to  have  unit  valency ;  it  is 
univalent.  Then  chlorin  is  univalent  also,  for  one 
volume  of  chlorin  combines  with  one  volume  of 
hydrogen.  As  two  volumes  of  hydrogen  unite  with 
one  volume  of  oxygen,  the  valency  of  oxygen  is 
twice  that  of  hydrogen  ;  it  is  bivalent.  Likewise,  the 
valency  of  nitrogen  and  of  carbon  is  triple  and  quad- 
ruple that  of  hydrogen,  respectively,  and  these  two 
elements  are  therefore  trivalent  and  quadrivalent. 
But  few  elements  exhibit  a  valency  of  more  than 
four. 

Radicals  also  have  a  valence.  Ammonium  (NH  4 ) 
and  hydroxyl  (OH)  are  univalent,  while  (SO4)  is 
bivalent. 


The  Atomic  Theory  —  Valence  145 

154.  Variable  Valency.  The  combining  power 
or  valency  of  an  element  is  not  always  the  same. 
Oxygen  in  water  is  bivalent,  but  in  hydrogen 
dioxid,  H2O2,  it  appears  univalent.  Also,  carbon, 
which  is  quadrivalent  in  methane,  CH4,  and  in  car- 
bon dioxid,  CO2,  seems  bivalent  in  carbon  mon- 
oxid,  CO.  Many  other  instances  of  variable  valency 
will  be  encountered  later.  Elements  exhibit  at 
times  one  valency  toward  certain  elements  and 
another  toward  other  elements.  Valence  is  prob- 
ably a  mutual  property  of  elements  and  depends 
upon  the  conditions  according  to  which  a  com- 
pound is  formed. 

Problems 

/.  The  valency  of  the  following  elements  is  indicated  by  the 
number  of  accents  :  Na'  (sodium),  K'  (potassium),  Ca"  (calcium), 
Al'"  (aluminum).  AVhat  are  the  formulas  of  the  chlorids  and  the 
oxids  of  each  of  the  elements,  if  chlorin  (Cl)  is  univalent  and 
oxygen  bivalent  ? 

.2. "-"If  one  liter  of  bromin  vapor  weighs  7.2^-,  and  if  one  gram 
of  hydrogen  combines  with  So&-  of  bromin,  what  is  the  valency  of 
bromin  ? 

j.  Balance  the  following  equations.  In  equations  (a)  to  (c)  a 
large  proportion  of  water  is  supposed  to  be  present  but  not  par- 
ticipating in  the  reaction. 

(a}     Zn  +          HC1  — ->          ZnCL,      +   H2. 

(zinc)  {hydrochloric  acid)  (zinc  chlorid} , 

(b)     Zn          +          H.SO.,      — >          ZnSO,     +  ? 

(sulfuric  acid)  (zinc  sulfate) 

(0     NaCl      +          H,SO4      —*         Na,SO4  +  HC1. 

(sodium  clilorid)  (sodium  sulfate) 

(d)  NaN03  +          H,SO,       — »         Na2SO4  +  HNO3. 

(sodium  nitrate) 

(e)  KC1O3     — >      KC1  +  O2. 


CHAPTER  XIV 

SALTS,  ACIDS,  AND  BASES 

Salts,  acids,  and  bases  are  so  common  and  valu- 
able, and  their  reactions  and  properties  are  of  such 
importance,  that  they  demand  attention  even  before 
some  of  the  elements  entering  into  their  composi- 
tion. 

155.  Early  Meaning  of  the  Terms  Salt,  Acid, 
Alkali,  and  Base.  Originally  the  word  "  salt  "was 
applied  to  common  table  salt  alone,  but  as  in  the 
course  of  time  other  substances  were  found  which 
resembled  table  salt  in  certain  particulars,  such  as 
color,  taste,  and  solubility,  the  same  name  was 
given  to  them  also,  often  with  the  qualification  of 
some  proper  noun,  as  Epsom  salt,  Rochelle  salt, 
Glauber's  salt. 

The  word  "  acid  "  signifies  sour,  and  was  given  to 
such  substances  as  possess  a  sour  taste.  Vinegar 
and  lemon  juice  were  among  the  first  acids  known. 

The  word  " alkali"  originally  meant  as/ics,  and 
was  the  name  given  to  the  soluble  constituents  of 
wood  ashes,  which  had  a  bitter,  brackish  taste  and 
a  soapy  feel.  It  was  later  found  that  acids  and 
alkalis  possessed  opposite  properties  in  several 
respects.  Thus,  litmus,  a  dyestufT  extracted  from 
certain  lichens,  is  turned  red  when  moistened  with 
an  acid  liquor,  and  blue  with  an  alkalin,  and  can 
be  made  to  change  color  any  number  of  times  by 
immersion  in  first  one  and  then  the  other  of  the 


Salts,  Acids,  and  Raises  147 

two  liquors.  Other  vegetable  extracts  also  undergo 
similar  changes  of  color.  It  was  also  found  that 
when  an  acid  solution  was  mixed  with  an  alkalin 
one,  for  certain  proportions  of  the  two  liquids  their 
mixture  did  not  affect  the  color  of  litmus,  and 
instead  of  tasting  sour  or  bitter,  tasted  salty.  The 
acid  and  alkali  neutralized  each  other's  properties, 
and  a  new  substance  was  formed  which  had  the 
general  properties  of  the  class  of  substances  known 
as  salts.  As  other  substances  were  found  to  behave 
like  alkalis  in  many  respects,  without  being  so  bit- 
ter and  corrosive,  the  name  of  alkali  was  gradually 
restricted  to  a  few  substances  only,  the  most  impor- 
tant of  which  are  caustic  soda  (sodium  hydroxid) 
and  caustic  potash  (potassium  hydroxid).  The  name 
of  "base"  was  then  assigned  to  the  whole  class  of 
substances  acting  like  alkalis  toward  acids,  i.  e., 
combining  with  them  to  form  salts. 

After  the  discovery  of  oxygen  and  hydrogen 
and  of  the  composition  of  water,  and  as  methods  of 
chemical  analysis  were  improved,  it  was  found  that 
all  acids  contained  hydrogen,  and  all  bases  both 
hydrogen  and  oxygen,  combined  in  the  radical, 
hydroxyl,  OH.  Furthermore,  salts  were  found  to 
be  composed  of  two "  parts,  one  of  a  metallic,  the 
other  of  a  non-metallic  nature. 

156.  Acid  Defined.  An  acid  is  a  compound 
which  has  usually  a  sour  taste,  changes  the  color  of 
many  substances,  as  litmus,  to  red,  and  reacts  with 
a  base  to  produce  a  salt  and  water.  It  is  composed 
of  a  non-metallic  element  or  radical  and  hydrogen ; 
the  hydrogen  can  be  replaced  by  a  metal  to  form 
a  salt. 


148  Elementary  Chemistry 

157.  Base  Defined.    A  base  is  a  compound  which 
restores  the  color  of  dyestuffs  that  has  been  changed 
by  an  acid,  and  reacts  with  an  acid  to  produce  a  salt 
and  water ;  it  is  composed  of  a  metal  or  metal-like 
radical  and  the  radical,  hydroxyl,  OH. 

158.  Alkali  Defined.     An  alkali  \$>  a  strong,  caus- 
tic base,  very  soluble  in  water.    Potassium  hydroxid, 
KOH,  sodium    hydroxid,  NaOH,  and    ammonium 
hydroxid,  (NH4)OH,  are  the  three  common  alkalis. 
The  first  two  are  sometimes  called  the  fixed  alkalis 
in  contradistinction  to  the  last,  which  is  called  the 
volatile  alkali,  as  heat  readily  vaporizes  it. 

159.  Salt  Defined.     A  salt  is  a  compound  usually 
without  action  on  vegetable  dyes.     It  may  be  pre- 
pared by  neutralizing  solutions  of   an  acid  and  a 
base,  as  well  as  in  other  ways  (Chapter  XVL).     It 
is  composed  of  a  metal  or  metal-like  radical  and  a 
non-metal  or  non-metallic  radical. 

THE  THEORY  OF  ELECTROLYTIC  DISSOCIATION.  The 
foregoing  definitions  represent  fairly  well  the  state  of 
our  knowledge  of  the  nature  of  acids,  bases,  and  salts 
up  to  the  year  1887,  when  Archgnius,  a  Swedish  chem- 
ist, brought  to  light  the  importance  of  a  certain  prop- 
erty of  salts,  acids,  and  bases,  and  ventured  a  hypothesis 
with  reference  to  it,  which  has  been  elaborated  into  a 
most  fruitful  theory.  This  property  is  that  of  electric 
conductance.  Hittorf,  indeed,  in  1840,  had  shown  that 
all  solutions  that  conduct  electricity  are  solutions  of 
salts,  acids,  or  bases,  but  this  attracted  little  attention  at 
that  time.  Arrhenius,  however,  brought  it  into  close  con- 
nection with  a  number  of  other  properties  of  solutions 
of  which  it  offers  a  simple  explanation.  It  also  gives 
a  simple  account  of  electric  conductance  in  solutions. 

ELECTRIC  CONDUCTANCE.  It  is  obvious  that  a  fluid 
may  be  transferred  from  one  place  to  another  in  two 
essentially  different  ways ;  it  may  flow  over  through 


Salts,  Acids,  and  Bases  149 

v 

pipes  or  it  may  be  carried  over  in  buckets.  Analo- 
gously, electricity  may  be  transferred  from  one  place  to 
another  in  two  ways.  The  flow  of  electricity  through 
or  along  a  metallic  wire,  (conductor  of  the  first  class) 
corresponds  to  the  first  way,  while  its  flow  through  a 
solution  (conductor  of  the  second  class)  corresponds  to 
the  second  way.  The  carriers  of  the  electricity  in  con- 
ductors of  the  second  class  are  the  two  parts  of  the  salt, 
acid,  or  base,  or  the  tons,  as  they  are  named. 

When  the  ends,  the  electrodes,  of  an  electrical  circuit 
are  at  a  different  electrical  level  or  potential  and  are 
immersed  in  any  solution  of  an  acid,  base,  or  salt,  the 
metallic  (hydrogen)  ions  or  cations  carry  the  positive 
electricity  towards  one  end  tof  the  circuit,  the  cathode, 
while  the  non-metallic  (hydroxyl)  ions  or  amons  carry 
the  negative  electricity  towards  the  other  end  of  the 
circuit,  the  anode.  Both  anions  and  cations  carry  equal 
and  definite  amounts  of  negative  and  positive  electri- 
city, respectively.  This  phenomenon  is  known  as  elec- 
trolysis, and  the  solution  is  called  an  electrolyte. 

It  is  natural  to  inquire  how  these  carriers  of  electri- 
city, these  ions,  come  into  existence  when  a  salt,  acid, 
or  base  is  dissolved,  for  these  compounds  when  per- 
fectly dry  do  not  conduct  electricity  at  all.  It  was 
formerly  supposed  that  they  were  formed  by  the  action 
of  the  electric  current,  but  Arrhenius  proposed  another 
explanation,  sometimes  called  the  lonization  Theory. 

THE  IONIZATION  THEORY.  Arrhenius  assumed  that 
when  a  salt,  acid,  or  base  dissolves,  the  very  act  of 
solution  breaks  it  up  more  or  less  into  its  ions.  The 
solvent  seems  to  act  much  as  a  change  of  temperature 
or  pressure  does  in  effecting  the  dissociation  of  a  com- 
pound. (Cf.  page  60.)  Just  as  a  rise  of  temperature  or 
diminution  of  pressure  causes  a  greater  and  greater 
degree  of  dissociation  of  many  substances,  so  does  an 
augmentation  of  the  proportion  of  the  solvent  in  a  solu- 
tion increase  the  degree  of  dissociation  of  the  dissolved 
substance  ;  for  infinite  dilutions  the  dissociation  is  com- 
plete, just  as  is  the  case  in  ordinary  dissociation  with 
infinitely  higlj  temperatures  or'low  pressures. 

To  distinguish  the  dissociation  of  a  salt,  acid,  or  base 
by  a  solvent  from  ordinary  dissociation,  the  former  is 


150  Elementary  Chemistry 

termed  electrolytic  dissociation,  and  Arrhenius'  loni- 
zation  Theory  is  often  called  the  Theory  of  Electrolytic 
Dissociation. 

How  A  SOLUTION  CONDUCTS  ELECTRICITY.  Suppose 
a  salt,  whose  metallic  part  we  shall  denote  by  M,  and 
non-metallic  part  by  A,  to  be  dissolved  in  water.  To 
simplify  matters  we  shall  assume  M  and  A  both  to  be 
univalent,  and  that  the  proportion  of  water  is  so  great 
that  the  salt  MA  is  practically  totally  dissociated  into 
its  ions.  This  dissociation  may  be  represented  by  the 
following1  equation  : 

MA  -^  M  +  A 

where  the  superposed  signs  -f-  and  —  mean  that  the 
respective  ions  are  charged  with  positive  and  negative 
electricity.  Inasmuch,  as  there  are  present  in  the  solu- 
tion the  same  number  of  cations  and  anions  charg-ed 
with  equal  quantities  of  electricity — the  cations  with 
positive,  the  anions  with  negative — the  solution  as  a 
whole  is  electrically  neutral.  If  now  two  electrodes  be 
placed  in  the  solution  and  a  current  of  electricity  passed 
through  it,  the  cations  will  be  attracted  by  and  move 
towards  the  negative  electrode,  and  the  anions  will  be 
attracted  by  and  move  towards  the  positive  electrode. 
There  will  thus  be  two  processions  of  ions  moving  in 
opposite  directions.  The  speed  with  which  they  move 
depends  mainly  upon  their  nature,  the  temperature,  and 
the  viscosity  of  the  solution. 

The  ions  on  arriving  at  the  electrodes  give  up  their 
electrical  charges  and  become  changed  into  electrically 
neutral  atoms  or  molecules,  which  may  react  with  the 
solvent  to  form  other  compounds  or  may  escape  from  it. 

The  foregoing  is  an  outline  of  what  is  supposed  to 
occur  in  the  electrolysis  of  any  soluble  salt.  If  there 
should  be  any  doubt  in  the  case  of  a  certain  substance 
as  to  what  the  two  parts  of  a  salt  are,  its  electrolysis  and 
subsequent  examination  of  the  electrodes  or  of  the 
solution  in  the  vicinity  of  the  electrodes  will  clear  up 
the  doubt. 

ACIDS,  BASES,  AND  SALTS  DEFINED  IN  TERMS  OF  IONS. 
Solutions  of  acids,  bases,  and  salts  alone  are  electrolytes. 
The  term  salt  includes  bases  and  acids.  In  addition  to 


Salts,  Acids,  and  Bases  151 

the  properties  already  given  as  characteristic  of  these 
classes  of  compounds,  the  following  statements  may  be 
made  : 

Salts  are  compounds  of  an  anion  and  a  cation. 

Acids  are  salts  whose  cation  is  ahvays  hydrogen,  not 
free  gaseous  hydrogen,  but  ionic  hydrogen.  The  general 
properties  of  acids  are  those  of  the  hydrogen  ion. 
Thus,  the  sour  taste  and  the  reddening  of  litmus  are 
done  by  the  hydrogen  ion,  no  matter  what  the  anion  it 
may  be  combined  with  to  form  the  acid. 

Bases  are  salts  whose  anion  is  ahvays  hydroxyl.  The 
general  properties  of  bases  are  those  of  the  ion, 
hydroxyl. 

SALTS,  ACIDS,  AND  BASES  COMPARED  IN  THE  LIGHT  OF 
THE  IONIZATION  THEORY.  Salts,  acids,  and  bases  have 
the  same  general  structure  ;  they  consist  of  an  electro- 
positive element  or  radical  (cation)  combined  with  an 
electro-negative  element  or  radical  (anion),  only  acids 
always  have  hydrogen  for  cation  and  bases  always 
hydroxyl  for  anion.  Acids  are  hydrogen  salts  ;  bases 
are  hydroxyl  salts.  All  three  classes  undergo,  electro- 
lytic dissociation  when  dissolved  in  water,  and  their 
solutions  conduct  electricity.  Acids  and  bases  unite  to 
produce  salts,  while  their  hydrogen  and  hydroxyl  ions 
combine  to  form  water.  Thus,  if  HA  and  C(OH)  rep- 
resent an  acid  and  base,  respectively,  their  reaction  is 
illustrated  by  the  equation  : 

(H  +  A)  +  (C  -J-  HO)  -»  (C  +  A)  +  H20 

160.     Acid,  Alkalin,  and  Neutral  Reactions.     A 

solution  is  said  to  have  an  acid  reaction  when  it 
tastes  sour  and  changes  the  color  of  such  substances 
as  blue  litmus  and  other  vegetable  colors.  It  is  said 
to  have  an  alkalin  ^reaction  when  it  tastes  bitter  and 
restores  the  color  of  the  substances  changed,  by 
acids.  A  solution  is  neutral  when  it  tastes  neither 
sour  nor  alkalin  and  has  no  effect  on  litmus.  Acid 
reactions  are  due  to  the  presence  of  hydrogen  ions ; 
Alkalin  reactions  to  the  presence  of  hydroxyl  ions. 


152  Elementary  Chemistry 

161.  Indicators.       Indicators    are    substances 
which  have   different   colors   in   acid   and   alkalin 
solutions.     The  requisites  of  a  good  indicator  are 
that   a   small   proportion  of  it  will  tinge  a  large 
amount   of    solution    and    will    change    its    color 
promptly  and  decidedly  when  the  solution  changes 
from  an  acid  to  an  alkalin  reaction,  and  vice  versa. 
Litmus  is  the   time-honored  indicator,  but  many 
others  are  known,  as.  Congo  red,  phenolphthalein, 
and  methyl  orange. 

162.  Nomenclature  of  Acids,  Bases,  and  Salts. 
Bases    are   called   hydroxids    of   metals,  as   sodium 
hydroxid,  NaOH,  and  calcium  hydroxid,  Ca(OH)2. 
The  names  of  acids  not  containing  oxygen  (Jiydra- 
cids]  are  distinguished  by  the  termination  "ic"  and 
the  prefix  "hydro,"  as  hydrochlorzV  acid.  The  names 
of  the  commonest  acids  containing  oxygen  (oxacids) 
also  terminate  in  "ic,"  as  sulfur^  acid,  H2SO4.  Acids 
-containing  less  oxygen  have  names  ending  in  "  ous," 
as   sulfun?^   acid,  H2SO3,  and   with   less   oxygen 
still,  the  prefix  "hypo"  is  added,  as  ////^chlorous 
acid,  HC1O.     Acids  containing  more  oxygen  than 
do  the  commoner  ones  have  names  beginning  with 
"per,"  as/<?rchloric  acid,  HC1O4. 

Salts  formed  from  hydracids  have  names  ending 
in  "id,"  as  sodium  chlorid,  NaCl.  The  nomencla- 
ture of  the  salts  of  the  oxacids  is  patterned  after 
that  of  the  acids,  thus : 

"ic"  acids  yield  "ate"  salts,  as  calcium  suites, 
CaS04. 

"ous"  acids  yield  "ite"  salts,  as  calcium  sulfz/V, 
CaSO3. 

The  prefixes  "hypo"  and  "per"  are  retained,  as 


Salts,  Acids,  and  Bases  153 

potassium  //j/<?nitrite,  KNO,  and  potassium  /^chlo- 
rate, KC1O4. 

IONS.  Much  of  chemistry  consists  in  the  study  of 
acids,  bases,  and  salts,  especially  when  dissolved  in 
water.  But  these  compounds  break  up  more  or  less 
into  their  ions  when  dissolved  in  water,  and  the  ions 
are  in  a  measure  independent  of  one  another.  Hence 
it  is  not  really  the  reactions  of  the  acids,  bases,  and 
salts  in  the  pure  state,  that  is,  free  from  water,  that  we 
study,  but  rather  the  reactions  of  their  ions.  It  is  nec- 
essary then  that  we  have  a  clear  idea  of  what  an  ion  is. 

THE  HYDROGEN  ION.  Ions,  as  such,  exist  only  in 
solution.  A  molecule  of  gaseous  hydrogen  is  a  very 
different  thing  from  an  ion  of  hydrogen.  With  the 
properties  of  the  hydrogen  molecule  we  have  already 
become  acquainted  (Chapter  IV.).  Some  of  the  proper- 
ties of  hydrogen  ions  are  these  :  (/)  They  can  exist  only 
in  solution,  and  then  only  when  an  equivalent  number  of 
ions  of  some  non-metallic  element  or  radical  is  present ; 
(2)  they  are  charged  with  enormous  quantities  of  positive 
electricity,  and  can  become  molecules  of  hydrogen  only 
W7hen  this  electrical  charge  is  neutralized  by  an  equal 
amount  of  negative  electricity  ;  ( j)  they  move  about  at 
random  in  the  solution,  but  when  a  current  of  electricity 
is  sent  through  it,  they  move  with  a  speed  depending 
upon  the  temperature  and  the  nature  of  the  solvent  to- 
ward the  negative  pole,  where  their  positive  charge  is 
neutralized  with  an  equal  negative  charge,  and  gaseous 
hydrogen  is  formed.  Analogous  properties  are  charac- 
teristic of  every  ion. 

THE  IONS  OF  THE  ELEMENTS  THUS  FAR  STUDIED. 
The  hydrogen  ion  is  that  which  characterizes  an  acid  as 
such,  and  has  been  described  above.  Oxygen  does  not 
form  simple  ions,  but  the  hydroxyl  ion  is  the  anion  of 
all  bases.  Nitrogen  does  not  assume  the  ionic  condition 
by  itself,  except  perhaps  in  hydrazoic  acid,  HN3.  The 
ammonium  radical  (NH4)  forms  a  cation  similar  in 
many  respects  to  those  of  potassium  and  sodium.  Car- 
bon also  does  not  assume  the  ionic  condition,  although 
the  radical,  cyanogen,  CN,  is  the  anion  of  hydrocyanic 
acid,  HCN. 


154  Elementary  Chemistry 

REACTIONS  OF  IONS.  The  reactions  between  bases, 
acids,  and  salts  in  aqueous  solution  are  almost  entirely 
reactions  between  their  ions.  Thus,  a  solution  of 
sodium  chlorid,  NaCl,  consists  largely  of  the  ions 

+ 
Na  and    Cl.     Likewise,  a    solution   of    silver  nitrate, 

+ 

AgNO3,  contains  a  large  number  of  Ag  and  NO3  ions. 
When  these  solutions  are  mixed,  silver  chlorid,  AgCl, 
which,  being  insoluble,  does  not  break  up  into  ions,  and 

+ 
sodium  nitrate,  NaNO3,  consisting  of  the  ions,  Na  and 

NO 3?  are  produced.  The  reaction  may  be  represented 
thus: 

(A+g+  N03)  +  (Na  +  Cl)  ->  AgCl  +  (Na  +  NO3) 

If,  however,  sodium  chlorate,  NaClO3,  which  consists 

+ 

mainly  of  the  ions  Na  and  C1O3,  be  added  to  a  solution 
of  silver  nitrate,  the  silver  chlorate  which  might  be 
formed  is  not  precipitated,  since  it  is  soluble  in  water. 
The  chlorin  in  sodium  or  silver  chlorate  is  not  an  ion 

itself,  but  is  a  part  of  the  chlorate  ion,  C1O3.  There  is 
no  apparent  result  then  when  the  solutions  of  silver 
nitrate  and  sodium  chlorate  are  mixed,  and  the  solution 
behaves  as  if  all  four  possible  combinations  of  the  ions 

4-       + 

Ag,  Na,  NO  3,  and  C1O3  were  present.  Many  other 
reactions  might  be  given  in  which  compounds  contain- 
ing the  same  element  react  differently  because  in  one 
of  the  compounds  the  element  is  in  one  ionic  condition, 
while  in  others  it  is  in  another. 

NOTE.  Most  of  the  substances  thus  far  studied  are  gases  or 
insoluble  solids,  and  hence  there  has  been  but  little  need  of  the 
lonization  Theory.  The  majority  of  substances  which  remain  to 
be  studied,  however,  are  salts,  acids,  or  bases,  and  to  be  consis- 
tent, perhaps,  the  theory  should  be  applied  in  a  thoroughgoing 
manner.  This  will  not  be  done,  however,  mainly  because  the 
theory  cannot  be  said  to  be  on  a  perfectly  sure  foundation,  and 
also  because  it  is  not  accepted  by  all  chemists  of  note.  It  is  an 
interesting  and  profitable  exercise,  nevertheless,  to  interpret 
reactions  in  terms  of  ions. 


CHAPTER  XV 

NITROGEN  OXIDS  AND  OXACIDS 

163.  Nature  of  Combination.  Nitrogen  com- 
bines with  oxygen  slowly  when  electric  sparks  are 
passed  through  a  mixture  of  the  two  gases  (Fig.  9). 
The  combination  takes  place  with  absorption  of 
heat  and  ceases  as  soon  as  the  passing  of  the  sparks 
is  stopped.  The  reason  for  this  behavior  is  that  the 
kindling  point  of  nitrogen,  i.  e.,  the  temperature 
at  which  nitrogen  starts  to  burn,  is  far  above  the 
temperature  produced  by  the  combustion.  This 
behavior  is  the  direct  opposite  of  that  observed  in 
the  union  of  hydrogen  and  oxygen  (page  44),  where 
the  combination  is  accompanied  with  an  evolution 
of  heat,  and  the  electric  spark  serves  only  to  start 
the  reaction  in  a  small  portion  of  the  mixture, 
which  then  spreads  rapidly  throughout  it. 

In  all,  there  are  five  oxids  of  nitrogen,  which 
offer  an  excellent  illustration  of  the  Law  of  Multiple 
Proportions,  but  seem  contrary  to  the  rules  of 
Valence.  The  oxids  of  nitrogen  do  not  occur  free 
in  nature  except,  perhaps,  in  small  amounts  during 
thunder  storms,  when  a  union  of  the  two  elements 
is  brought  about  by  lightning  flashes.  The 
ammonia  which  may  also  be  formed  during  the 
storm  generally  combines  with  the  oxids.  The 
method  commonly  used  in  their  preparation  con- 
sists in  decomposing  nitric  acid  or  nitrates  by  the 
action  of  heat  alone  or  aided  by  some  metal  or  acid. 

[155] 


156  Elementary  Chemistry 

NITROUS  OXID,  NoO 

164.  Preparation.     When  ammonium  nitrate, 
a  compound  of  ammonia  and  nitric  acid,  is  heated 
to  about  200°,  it  decomposes  into  nitrous  oxid  and 
water : 

NH4NO3  ->  N2O  +  2H2O 

If  the  temperature  is  above  300°,  nitric  oxid  is 
also  formed  in  small  amounts. 

165.  Properties.    Physical.     Nitrous   oxid   is  a 
colorless   gas   of  a  sweetish  taste  and  a  pleasant 
odor.     It  is  soluble  in  somewhat  less  than  its  own 
volume  of  water. 

Chemical.  Nitrous  oxid  supports  the  combustion 
of  wood,  phosphorus,  and  most  other  substances 
quite  as  well  as  does  oxygen,  but  as  the  substances 
have  a  higher  kindling  temperature  in  it  than  in 
oxygen,  they  need  to  be  well  ignited  before  being 
introduced  into  the  gas.  The  equation  for  the 
combus-tion  of  carbon  in  this  gas  is : 

2N20  +  C  ?=  C02  +  2N2 

Physiological.  When  mixed  with  about  a  quarter 
of  its  volume  of  oxygen  (air)  and  inhaled,  nitrous 
oxid  produces  a  peculiar  intoxication  ^and  excites 
laughter;  hence  the  popular  name  of  " laughing 
gas."  When  inhaled  in  the  pure  state,  it  produces 
intoxication,  then  insensibility,  and  ultimately 
death.  It  supports  respiration  longer  than  any 
other  gas  except  oxygen. 

COMPOSITION.  Equal  volumes  of  nitrous  oxid  and 
of  hydrogen  are  mixed  and  exploded  in  an  eudiom- 
eter. There  results  a  contraction  of  one-half,  and  the 
residual  gas  is  found  to  be  nitrogen.  The  contraction 


Nitrogen  Oxids  and  Oxacids  157 

represents  the  volume  of  water  vapor  formed,  and  as 
one  volume  of  water  vapor  consists  of  one  volume  of 
hydrogen  and  one-half  volume  of  oxygen,  one  volume 
of  nitrous  oxid  contains  one  volume  of  nitrogen  and 
one-half  volume  of  oxygen.  As  the  weight  of  one  liter 
of  this  gas  is  1.965^-  it  follows  that  its  formula- is  N2O, 
for  1,965  =  2  x  0.625  (the  elemental  weight  of  nitrogen) 
+  0.715  (the  elemental  weight  of  oxygen). 

166.  Uses.  Nitrous  oxid  is  used  by  dentists 
to  produce  insensibility  during  the  extraction  of 
teeth.  For  that  purpose  it  is  liquefied  and  stored 
in  strong  cylinders  provided  with  stopcocks. 

HEAT  OF  FORMATION  OF  NITROUS  OXID.  Both  hydro- 
gen and  carbon  burn  much  more  vigorously  in  nitrous 
oxid  than  they  do  in  oxygen,  and  consequently  the  lib- 
eration of  heat  must  be  greater.  This  indicates  that 
the  heat  of  formation  of  this  oxid  of  nitrogen  is  neg- 
ative ;  it  is  an  endothermic  compound.  Its  heat  of 
formation  has  then  to  be  determined  indirectly.  How 
this  is  done  is  illustrated  by  the  following  thermochem- 
ical  equations,  in  which  the  formula  weights  of  the  sub- 
stances are  used  : 

FIRST  METHOD 

(r)     H2  -}-  N2O  =  H2O  -f  N2  -f  86,400  calories. 
(2)  H2  -f-  O  =  H2O  -f  68,400  calories. 

By  subtraction  of  (2)  from  (i)  and  transposition. 
(j)  N2  -f  O  =  N2O  —  18,000  calories. 

SECOND  METHOD 

(1)  CO  -j-  N2O  =  CO2  +  N2  +  85,400  calories. 

(2)  CO  -f  O  =  CO2  -j-  68,000  calories. 

By  subtraction  of  (2)  from  (i)  and  transposition, 
(j)  N2  +  O  —  .N2O  —  17,400  calories. 

Both  of  these  calculations  are  based  on  experimental 
results,  which  are  of  course  subject  to  error.  Taking 
their  average,  we  have  17,700  calories  as  the  heat  ab- 
sorbed in  the  formation  of  44^-  of  nitrous  oxid. 


.  158  Elementary  Chemistry 

<  . 

NITRIC  OXID,  NO 

167.  Preparation.     When  dilute  nitric  acid  is 
brought   in   contact  with   many  metals,  especially 
copper,  mercury,  or    silver,  reaction    takes    place 
readily,  and  nitric  oxid  is  the  main  gaseous  prod- 
uct.   It  may  also  be  obtained  by  the  action  of  nitric 
acid  on  ferrous  sulfate  (green  vitriol). 

168.  Properties.     Physical.      Nitric   oxid  is   a 
colorless  gas,  the  taste  and  odor  of  which  cannot  be 
ascertained,  as  it  combines  with  oxygen  on  coming 
in  contact  with  the  air,  forming  the  tetroxid. 

Chemical.  While  but  slightly  soluble  in  water, 
nitric  oxid  is  very  soluble  in  a  solution  of  ferrous 
sulfate,  with  which  it  forms  a  brown  compound  of 
the  two  substances.  As  nitric  oxid  decomposes  at 
temperatures  above  600°,  some  substances  may  be 
made  to  burn  in  it,  provided  their  heat  of  combus- 
tion is  sufficient  to  decompose  the  oxid  of  nitrogen. 
Thus,  phosphorus,  if  ignited  and  introduced  into 
the  gas,  will  continue  to  burn,  while  sulfur  and 
charcoal  will  not.  Nitric  oxid  combines  readily 
with  oxygen  to  form  nitrogen  dioxid,  a  deep  brown 
gas  quite  soluble  in  water. 

NOTE.  Priestley  in  1772  observed  that  when  one  volume  of 
nitric  oxid  was  mixed  with  two  volumes  of  air  in  a  tube  over  water 
*  there  was  a  diminution  of  one-fifth  of  a  volume.  This  observa- 
tion was  made  before  the  discovery  of  oxygen  ;  hence  he  could  not 
draw  the  conclusion  that  we  can  to-day,  viz. ,  that  one-fifth  of  the 
volume  of  the  air  is  oxygen. 

COMPOSITION.  One  volume  of  nitric  oxid,  when 
heated  with  sodium  or  finely  divided  iron  or  copper, 
undergoes  a  diminution  of  one-half.  The  residual  gas 
is  nitrogen ;  the  oxygen  has  combined  with  the  metal. 
Nitric  oxid  therefore  contains  equal  volumes  of  nitrogen 


Nitrogen  Ox  ids  and  Ox  acids  159 

and  oxygen.  One  liter  weighs  1.34^-,  which  is  equal  to 
the  sum  of  0.625  (the  elemental  weight  of  nitrogen)  and 
0.715  (the  elemental  weight  of  oxygen). 

169.  Uses.     The  property  that  nitric  oxid  has 
of  combining  directly  with  oxygen  plays  a  funda- 
mental role  in  the  manufacture  of   sulfuric  acid; 
great  quantities  of  it  are  used  in  that  process. 

170.  Nitrogen   Trioxid,  N2O3.      Nitrogen   tri- 
oxid  is  obtained  as  a  blue  liquid  when  nitric  oxid 
is  passed  into  liquefied  nitrogen  tetroxid,  N2O4,  at 
temperatures  below  -21°.     It  decomposes  at  higher 
temperatures  into  a  mixture  of  nitrous  and  nitric 
oxids. 

171.  Nitrogen  Pentoxid.     Nitrogen  pentoxid  is 
prepared  by  the  action  of  phosphorus  pentoxid  on 
very  concentrated  nitric  acid  at  low  temperatures. 
It  is  a  white,  crystalline  substance  melting  at  30° 
with  partial  decomposition,  while  at  47°  it  decom- 
poses rapidly  into  oxygen  and  nitrogen  dioxid. 

172.  Nitrogen  Dioxid  and  Tetroxid  (Peroxid). 
Nitrogen  dioxid  and  tetroxid  may  be  prepared  (/)  by 
mixing  two  volumes  of  nitric  oxid  with  one  of  oxy- 
gen, and  (2)  by  heating  lead  or  manganous  nitrate. 

At  low  temperatures  nitrogen  peroxid  is  a  color- 
less solid,  melting  at  -12°  into  a  light  yellow  liquid 
which,  as  the  temperature  rises,  assumes  a  deeper 
and  deeper  tint.  At  25°  the  liquid  boils,  giving 
off  a  vapor  of  a  reddish-brown  color.  The  color  of 
this  vapor  deepens  as  the  temperature  continues 
to  rise,  until  at  50°  it  is  so  brown  as  to  be  almost 
opaque.  When  the  temperature  is  lowered,  the 
reverse  changes  occur;  we  have  to  do  with  a  rever- 
sible reaction. 


i6o 


Elementary  Clicmistry 


NITRIC  ACID 

173.  Occurrence.  Free  nitric  acid  is  not  met 
with  in  nature  except  in  minute  amounts  in  the  air 
after  thunder  storms.  It  usually  combines  with  the 
ammonia  which  has  also  been  formed  by  the  action 

of  the  lightning 
flashes,  and  the 
resulting-  com- 
pound, ammo- 
nium nitrate,  is 
washed  down  in 
the  soil.  Com- 
pounds of  nitric 
acid  with  the 
metals  sodium  - 
and  potassium  ( 

Fig.    32 A    CONVENIENT    ARRANGEMENT    OF    APPA-         clTQ        I  O  U  U  Q 

RATUS    FOR    PREPARING    NITRIC     ACID 


certain  places,  and  are  known  as  niters  or  saltpctcf 
These  compounds  are  formed  by  the  action 
microorganism  upon  substances  of  animal  an 
etable  origin  containing  compounds  of  nitro 
well  as  of  potassium  and  sodium.        .Q  L/ 

HISTORICAL  NOTE.      The  old  chemists  catted  nitric     Y 
acid  "  spirits  of  niter  "  because  it  was  formecf  as  vapor  "* 
("spirit")  when  niter  was   heated  with   alum,  w-h^ch 
contains  sulfuric  acid  in  combination.     Became  of  its 
great  corrosive  powers  it  was  also  called  "aqiia_fortts." 

174.  Preparation.  Nitric  acid  is  made  by  the 
action  of  strong  sulfuric  acid  on  sodium  or  potas- 
sium nitrate ;  manufacturing  plants  employ  essen- 
tially the  same  process ;  sodium  nitrate  is  used,  as 
it  is  cheaper  than  potassium  nitrate. 


Nitrogen   Ox  ids  and  Oxacids  161 

NaN03  +  H2S04  ->  HNaSO4  +  HNO3 

The  nitric  acid  thus  obtained  is  not  pure ;  it  is 
contaminated  with  nitrogen  peroxid,  which  is  shown 
by  its  yellow  color.  It  is  purified  by  distillation, 
yielding  a  distillate  containing  about  60  per  cent 
of  the  pure  acid.  If  carefully  dried  saltpeter  and 
concentrated  sulfuric  acid  be  used,  the  nitric  acid 
obtained  is  very  nearly  100  per  cent  pure.  If  the 
heating  is  done  under  diminished  pressure,  the  yield 
and  the  purity  of  the  acid  is  increased. 

175.  Properties.  PJiysicaL  Pure  nitric  acid  is 
a  colorless  liquid  with  a  very  pungent  odor,  miscible 
in  all  proportions  with  water. 

Chemical.  At  a  red  heat  nitric  acid  is  decomposed 
into  water,  oxygen,  and  nitrogen  peroxid  ;  sunlight 
effects  the  same  decomposition  slowly.  It  is  very 
corrosive ;  but  few  substances  withstand  its  attack. 
It  dissolves  most  metals,  forming  nitrates,  all  of 
which  are  soluble  in  water.  It  is  a  powerful  oxid- 
izing agent,  and  stains  the  nails  and  flesh  yellow. 

REDUCTION  OF  NITRIC  ACID.  When  nitric  acid  acts 
upon  metals,  the  hydrogen  we  might  expect  to  be 
evolved  at  first  in  accordance  with  the  equation  : 

Cu  -f  2HNO3  — >  H2  +  Cu(NO3)2 
(copper)  (copper  nitrate) 

reacts  with  the  acid,  depriving  it  of  some  of  its  oxygen 
and  forming  certain  of  the  oxids  of  nitrogen.  These 
reactions  may  be  shown  by  the  following-  equations: 

2  HN03  -f     H2  — >  2  H20  +  2  N02 
2  HN03  +  2  H2  — >  3  H20  +     N203 
2  HNO3  H-  3  H2  — »  4  H2O  +  2  NO 
2  HNO3  +  4  H9"  — >  5  H2O  +     N2O 
2  HN03  +  5  H"2  — >  6  H20  -f     N7 
,.,  HN03  4-  4H2  — >  3H2O  +     NH3 


1 62  Elementary  Chemistry 

Which  of  these  reactions  will  predominate  depends 
upon  the  nature  of  the  metals,  the  strength  of  the  acid, 
the  temperature,  and  on  the  amount  of  the  nitrate  of 
the  metal  which  is  already  formed.  For  example,  when 
copper  is  used,  at  first  some  nitrogen  tetroxid  is  formed, 
then  nitrogen  dioxid  and  monoxid  (only  a  little),  and 
usually  a  very  little  nitrogen.  During  the  course  of 
the  reaction  several  of  these  oxids  may  be  simultane- 
ously formed.  By  repeated  trials,  however,  it  has  been 
ascertained  what  particular  conditions  must  be  observed 
in  order  to  give  a  predominance  to  one  oxid. 

176.  Fuming  Nitric  Acid.     Nitrogen  dioxid  is 
quite  soluble  in  nitric  acid ;  the  solution  has  a  red 
color  and  gives  off  reddish  fumes,  whence  the  name. 

Fuming  nitric  acid  is  prepared  by  heating  to  a 
high  temperature  potassium  nitrate  and  sulfuric 
acid.  All  the  hydrogen  is  thereby  expelled  from 
the  sulfuric  acid : 

2  NaNO3  +  H2S04  J-*  Na2SO4  +  2  HNO3 

Much  of  the  nitric  acid  dissociates,  however,  at 
this  higher  temperature,  and  the  NO2  dissolves  in 
the  distillate : 

4HNO3  -^4NO2  +  2H2O  +  O2 

By  virtue  of  the  dissolved  dioxid  this  acid  has 
even  a  more  powerful  oxidizing  action  than  pure 
nitric  acid. 

177.  Uses.     Nitric  acid  is  used  in  making  sul- 
furic acid,  nitrobenzene,  gun  cotton,  nitroglycerin, 
and  celluloid.     It  is  employed  in  etching  on  copper 
and  in  producing  yellow  patterns  on  woolen  goods. 

178.  Nitrous  Acid.     Nitrous  acid  may  be  pre- 
pared by  dissolving  nitrogen  trioxid  or  dioxid  in 
water ;  nitric  acid  also  is  formed  in  the  latter  case, 


Nitrogen  Oxids  and  Oxacids  163 

and  by  the  action  of  dilute  sulfuric  acid  on  a  very 
dilute  solution  of  sodium  nitrite : 

H,S04  +  2NaN02  -»  Na2SO4  +  2HNO2 
Nitrous  acid  is  quite  unstable,  and  is  of  no  prac- 
tical importance,  although  certain  of  its  compounds 
with  metals,  such  as  sodium  nitrite,  are  used  in 
various  experiments  in  the  laboratory  and  in  the 
manufacture  of  dyestuffs. 

Exercises 

/.     How  may  oxygen  and  nitrous  oxid  be  distinguished? 

2.  When  ammonia  and  air  are  heated  and  passed  over  the 
catalytic  agent  (platinum  sponge),  nitric  acid  is  formed.  What 
does  this  prove  as  to  the  composition  of  nitric  acid  ? 

j.  If  nitric  acid  be  boiled  and  its  vapor  passed  through  a 
tube  containing  red-hot  copper,  water  and  nitrogen  pass  out  of 
the  tube.  What  light  does  this  fact  throw  upon  the  composition 
of  nitric  acid  ? 

4.  What  happens  to  nitric  acid  when  passed  through  a  red- 
hot  tube  ? 

5.  Why  does  even  the  purest  of  nitric  acid  turn  yellow  and 
even  brown  on  standing  in  a  lighted  room  ? 

6.  What  is  the  effect  of  heat  upon  (a)  potassium  nitrate  ?    (&) 
lead  nitrate?    (c)  ammonium  nitrate? 

Problems 

/.  How  much  nitric  acid  has  to  be  decomposed  in  order  to 
yield  100  s-  of  oxygen  ? 

2.     Turner,  in  1833,  obtained  from  222.884^- of  silver  nitrate, 
AgNO3,  1 88. 050^- silver  chlorid,  AgCl.     The  atomic  weights  of 
silver,  oxygen,  and  chlorin  are  107.94,  16.00,  and   35.45,  respec- 
tively.    What  is  the  atomic  weight  of  nitrogen? 
j.     Penny,  in  1839,  converted 

I.     291.439  g.  KC1O3  into  240  553  g-  KNO3 
II.     420.064^-- KC1      into  569. 756  <£-•  KNO3 
III.     448.270^.  KNO3  into  330.496  £••  KC1 

The  atomic  weights  of  potassium,  chlorin,  and  oxygen  are 
39.14,  35.45,  and  16.00,  respectively.  Calculate  in  each  series  of 
determinations  the  atomic  weight  of  nitrogen. 


CHAPTER  XVI 

PREPARATION    AND    PROPERTIES    OF 
ACIDS,   SALTS,   AND    BASES 

A  large  number  of  the  reactions  which  remain 
to  be  studied  have  to  do  with  the  preparation  of 
salts,  acids,  and  bases,  and  it  is  accordingly  well  to 
give  a  preliminary  account  of  the  general  princi- 
ples governing  such  preparations.  In  most  of  the 
methods  employed  the  compounds  are  obtained  in 
solution,  and  to  obtain  them  in  a  state  of  purity  the 
water  has  to  be  removed  by  evaporation  and  the 
compounds,  when  they  are  solid,  crystallized  out. 

PREPARATION   OF   SALTS 

179.  By   Direct   Union   of  Elements.    Many 
metals  unite  directly  with  non-metals  to  form  salts. 
Thus,  if  chlorin  be  passed  over  sodium,  common 
table  salt  (sodium  chlorid)  is  produced;   mercury, 
iron,  and  other  metals  also  combine  directly  with 
the  halogens.     Many  metals  "burn"  in  chlorin  gas 
with  almost  as  much  brilliancy  as  in  oxygen. 

180.  By  Action  of  an  Acid  on  a  Metal.    Many 
soluble  salts  may  be  prepared  by  dissolving  a  metal 
in  an  acid.     The  metal  combines  with  the  anion  of 
the  acid,  forming  the  salt  which  remains  dissolved. 
Insoluble  salts  cannot  usually  be  made  in  this  way, 
for  the  salt  which  may  be  produced  when  the  metal 
and  acid  are  first  brought  together,  forms  a  coating 
over   the  metal,    thus   protecting  it   from   further 

[164] 


Acids,  Salts,  and  Bases  165 

action.  Besides  the  salt,  hydrogen  is  also  produced, 
and  this  may  react  with  the  acid  to  give  rise  to 
other  substances.  Thus,  nitric  acid  is  reduced  by 
metals  (§  175),  as  is  also  the  case  with  strong  sulfuric 
acid,  but  with  no  evolution  of  hydrogen. 

181.  By  Action  of  an  Acid  on  a  Base;  Neutral- 
ization. When  solutions  of  an  acid  and  of  a  base 
are  brought  together  the  anion  of  the  acid  com- 
bines with  the  cation  of  the  base  to  form  a  salt, 
while  the  hydrogen  of  the  acid  and  the  hydroxyl  of 
the  base  unite  to  form  water. 

According  to  the  theory  of  electrolytic  dissoci- 
ation a  soluble  acid  or  base  is  more  or  less  dis- 
sociated into  its  ions  by  the  very  act  of  solution. 
When  a  solution  of  an  acid  is  mixed  with  a  solution 
of  a  base,  since  both  the  compounds  are  already 
ionized,  the  mixing  would  merely  affect  the  degree 

of  ionization.     As  water,  however,  dissociates  but 

+ 
very  slightly  into  its  ions,  H  and  OH,  the  hydrogen 

and  hydroxyl  ions  contained  in  the  acid  and  base 
unite  to  form  water,  when  the  solutions  are  mixed, 
and  the  main  chemical  reaction  in  neutralization  is 
the  formation  of  water.  The  equations  for  a  num- 
ber of  neutralization  reactions  are  the  following  : 

(Na  +  OH)  +  (  H  +  Cl)      -^  (Na  +  Cl)      +  H  2O 
(K  +  O~H)  +  (H  +  Cl)      -^    (K  +  C1)      +  H2O 

(Na  +  OH)  +  (H  +  N03)  -+  (Na  +  NO3)  +  H2O 
(H  +  N03)->    (K  +  N~03)  +  H20 


Many  more  similar  equations  could  be  written,  but 
enough  are  probably  given  to  show  the  mechanism 


1 66  Elementary  Chemistry 

of  the  reaction.  The  left  members  always  contain 
hydrogen  and  hydroxyl  ions  together  with  the 
cation  of  the  base  and  the  anion  of  the  acid.  In 
the  right  member  the  latter  remain  unchanged, 
while  the  hydrogen  and  hydroxyl  ions  unite  to 
form  water. 

If  in  the  phenomenon  of  neutralization  the  chief 
chemical  action  is  the  formation  of  water,  the 
energy  changes  due  to  neutralization  should  be 
the  same  when  such  quantities  of  acid  and  base 
are  used  as  produce  equal  amounts  of  water.  And 
this  deduction  has  been  found  to  be  true. 

182.  By  Action  of  an  Acid  on  Salts.     Examples 
of  this  reaction  have  been  discussed  on  page  78, 
and  others  will  be  considered  later.     A  favorite  salt 
is  the  carbonate,  as  the  carbon  dioxid  produced  is 
gaseous  and  therefore  easily  separated  from   the 
salt  desired.     Thus,  the  reaction  between  calcium 
carbonate  (marble)  and  hydrochloric  acid  to  give 
calcium  chlorid,  CaCl2,  carbon  dioxid,  and  water 
may  be  represented  by  the  equation  : 

CaCO3  +  2HCl->CaCl2  +  CO2  +  H2O 

PREPARATION   OF   ACIDS 

183.  General  Method.     The  general  method  of 
preparation  of  an  acid  consists  in  heating  a  salt  with 
another  acid  of  higher  boiling  point.     Sulfuric  acid 
is  less  volatile  than  most  other  acids,  and  hence 
usually  employed.      The  oxids  of  the  non-metals, 
as  sulfur  and  phosphorus,  react  with  water  to  pro- 
duce acids. 

"STRENGTH"  OF  AN  ACID.  The  true  measure  of  the 
"strength"  of  ail  acid  is  not  its  ability  to  displace 


Acids,  Salts,  and  Bases  167 

another  acid  from  a  salt,  when  the  first  acid  i  nd  the 
salt  are  heated  together,  for  that  ability  depends  almost 
wholly  upon  the  relative  volatility  of  the  two  acids. 
The  true  measure  of  the  "strength"  of  acids  is  rather 
their  degree  of  ionization  in  solution.  Under  like  con- 
ditions of  dilution,  sulfuric  acid  is  only  about  half  as 
much  ionized  as  either  nitric  or  hydrochloric  acid,  and 
hence  is  really  but  about  half  as  "strong." 

PREPARATION   OF   BASES 

184.  Soluble    Bases.     Soluble    bases    may    be 
made    by    the    action    of    slaked   lime    or   caustic 
alkalis  on  certain  salts  of  the  base  required.     Gen- 
eral rules  can  hardly  be  given ;  each  case  must  be 
considered  by  itself. 

185.  Insoluble  Bases.     Insoluble  bases  are  pre- 
pared   by    mixing    two    solutions,   one    of    which 
contains  hydroxyl  ions  and   the  other  cations   of 
the  base  desired.     Thus,  the  insoluble  base,  iron 
hydroxid,  Fe(OH)2,  can  be  prepared  by  adding  a 
solution  of  potassium  hydroxid,  KOH,  to  a  solution 
of   iron    sulfate,  FeSO4,  although  any  other  iron 
(ferrous)   soluble   salt   would  do  as  well  and  any 
other  soluble  hydroxid. 

HYDROLYSIS.  A  number  of  salts  are  known  which 
have  a  "basic  or  acid  reaction  in  solution.  All  such  salts 
are  made  up  of  a  strong  base  combined  with  a  weak 
acid  or  a  weak  base  combined  with  a  strong  acid.  Now 
the  strength  of  a  base  or  of  an  acid  depends  upon  its 
degree  of  ionization.  When  a  salt  made  up  of  a  strong 
base  and  a  weak  acid  is  dissolved  in  water,  although 
there  are  some  hydrogen  ions  present,  the  number  of 
hydroxyl  ions  is  so  much  larger  that  the  solution  as 
a  whole  shows  a  basic  behavior  and  gives  an  alkalin 
reaction.  Likewise,  a  salt  composed  of  a  weak  base 
and  a  strong  acid  is  dissociated  into  so  many  more 
hydrogen  than  hydroxyl  ions  that  its  reaction  is  acid. 


CHAPTER  XVII 

THE  HALOGENS;  THEIR  HYDROGEN  AND 
OXYGEN  COMPOUNDS 

The  name  " halogen"  (from  two  Greek  words, 
meaning  salt-producer)  is  given  to  the  closely  related 
group  of  elements,  fluorin,  chlorin,  bromin,  and 
iodin,  because  these  elements  combine  directly  with 
many  metals  to  form  compounds  known  as  halid 
salts,  or  simply  Jialids. 

CHLORIN 

HISTORICAL  NOTE.  Free  chlorin  was  first  obtained 
by  Scheele  in  1774  by  heating  hydrochloric  acid  with 
manganese  dioxid.  A  little  later,  Berthollet  observed 
that  its  aqueous  solution  gave  off  oxygen  when  exposed 

tto  sunlight,  and  he  therefore  drew  the  erroneous  con- 
clusion that  chlorin  contains  oxygen.  In  1 8 10,  however, 

>  Davy  proved  the  absence  of  oxygen  in  the  substance, 
and  Gay-Lussac,  who  also  independently  arrived  at  the 
same  conclusion,  gave  the  name  of  chlorin  (from  a 
Greek  word,  meaning  green]  to  the  new  element. 

186.  Occurrence.     Free  chlorin  is  not  met  with 
in  nature.     Its  compounds  with  sodium,  potassium,' 
and  magnesium  are  very  abundant,  however,  form- 
ing the  larger  part  of  the  residue  left  after  the  evap- 
oration of  sea  water.     The  beds  of  dried-up  seas 
and  lakes,  therefore,  consist  largely  of  chlorin  salts. 

187,  Preparation.     A  compound  rich  in  oxygen, 
as   manganese    dioxid,  MnO2,  lead    dioxid,  PbO2, 
potassium  dichromate,  K2Cr2O7,  or  potassium  chlo- 
rate, KC1O3,  is  heated  with  hydrochloric  acid.     The 
acid  is  oxidized,  its  hydrogen  unites  with  the  oxygen 

[168] 


TJic  Halogens  169 

to  form  water,  and  a  part  of  the  chlorin  is  set  free ; 
the  rest  of  the  chlorin  combines  with  the  metal  to 
form  a  salt : 

MnO7  +    4HCl-»MnCl2  +  2H2O  +  C12 
PbO2  +    4HCl->   PbCl2  +  2H2O+C12 

K2Cr2O7  +  HHCl 

->  2  KC1  +  2  CrCl3  +  7  H20  +  3  C12 

Instead  of  first  preparing  hydrochloric  acid  and 
then  letting  it  react  with  the  oxidizing  agent,  the 
hydrochloric  acid  may  be  formed  by  the  reaction  of 
sulfuric  acid  on  salt,  which,  as  soon  as  it  is  formed, 
is  oxidized  by  the  oxidizing  agent,  usually  manga- 
nese dioxid : 
Mn02  +  2H?S04  +  2NaCl 

— >  MnSO4  +  2H2O  +  Na2  SO4  +  C12 

Chlorin  may  also  be  obtained  by  the  action  of 
strong  hydrochloric  acid  on  bleaching  powder, 
and  by  the  electrolysis  of  some  metallic  chlorid,  ^ 
such  as  sodium  chlorid  ;  graphite  electrodes  are 
used,  since  chlorin  attacks  metallic  ones. 

188.  Manufacture  Chlorin  gas  is  used  in  sev- 
eral industries  in  large  amounts.  Several  technical 
processes  have  been  devised  to  utilize  in  a  more  or 
less  direct  manner  the  oxygen  of  the  air  to  effect 
the  oxidation  of  hydrochloric  acid. 

DEACON'S  PROCESS.  A  mixture  of  hydrogen  chlorid, 
HC1,  and  air  is  conducted  through  heated  tubes  filled 
with  fragments  of  burnt  clay  impregnated  with  some 
salt  of  copper.  The  copper  salt  acts  catalytically  so 
that  steam  and  chlorin  pass  out  of  the  tubes.  The 
reaction  is  not  well  understood,  but  it  really  amounts  to 
an  oxidation  of  hydrogen  chlorid  : 

4HC1  +  O,-*  2H20  +  2C12 


170  Elementary  Chemistry 

As  air  contains  nitrogen,  the  chlorin  thus  obtained  is 
mixed  with  about  70  per  cent  of  that  gas,  which,  how- 
ever, is  of  little  moment  in  many  industrial  applications. 
WELDON  PROCESS.  The  soluble  manganous  chlorid, 
MnCl2,  which  is  formed  when  manganese  dioxid  acts 
on  hydrochloric  acid,  is  treated  with  slaked  lime  : 

MnCl2  -f  Ca(OH)2  — »  CaCl2  +  Mn(OH)2 

Soluble  calcium  chlorid,  CaCl2,  and  insoluble  manganous 
hydroxid,  Mn(OH)2,  are  produced.  A  current  of  air  is 
forced  'through  the  mixture  whereby  the  manganous 
hydroxid  is  oxidized  to  manganous  acid  : 

2  Mn(OH)2  +  O2  — >  2  H2MnO3 

The  manganous  acid  combines  with  the  calcium  hy- 
droxid present  to  form  insoluble  calcium  manganite  : 

H2MnO3  +  Ca(OH)2  — >  CaMnO3  +  2  H2O 

The  calcium  manganite  is  filtered  and  treated  with 
hydrochloric  acid  ;  chlorin  is  thus  obtained  : 

CaMn03  +  6  HC1  — >  MnCl2  +  CaCl2  +  3  H2O  +  C12 

The  manganous  chlorid  is  thus  seen  to  be  regenerated 
and  can  again  be  subjected  to  the  same  process  as 
above.  It  is  also  apparent  that  the  oxidation  is  effected 
by  atmospheric  oxygen.  A  disadvantage  of  the  method 
is  the  loss  of  about  two-thirds  of  the  chlorin  in  the 
hydrochloric  acid,  for  the  calcium  chlorid  which  is 
formed  is  almost  valueless. 

MAGNESIUM  CHLORID  PROCESS.  Magnesium  chlorid 
occurs  in  considerable  quantities  in  the  mineral  car- 
nallite,  MgCl2*  KC1,  and  is  also  obtained  from  other 
sources.  When  heated  with  steam  it  yields  hydrochloric 
acid  : 

MgCl2  +  H20  -»  MgO  +  2  HC1 

When  heated  in  the  absence  of  water  in  a  current 
of  air,  it  gives  chlorin ': 

2  MgCl2  +  O2  — >  2  MgO  -f  2  C12 

ELECTROLYTIC  PROCESSES.  Both  in  Castner's  and  in 
Acker's  electrolytic  methods  of  manufacturing  sodium 
hydroxid  (page  187)  chlorin  is  evolved  at  one  pole. 


The  Halogens  171 

189.  Properties.  Physical.  (Table  L,  Appendix 
D.)  Chlorin  is  a  greenish-yellow  gas  with  a  very 
disagreeable  smell.  It  is  soluble  in  about  a  third 
of  its  volume  of  water. 

Chemical.  Chlorin  combines  directly  with  all  but 
some  rare  elements  and  oxygen,  nitrogen,  carbon, 
and  fluorin,  although  by  indirect  methods  com- 
pounds of  the  elements  specified  can  be  obtained. 
Hydrogen  and  chlorin  do  not  combine  at  low  tem- 
peratures and  in  the  dark ;  they  do  so,  however,  at 
high  temperature,  and  with  explosive  violence  when 
exposed  to  sunlight.  Hydrogen,  as  well  as  many 
metals,  "burn"  in  the  gas.  Aqueous  solutions 
decompose  slowly  when  exposed  to  light;  the 
hydrogen  combines  with  the  halogen  to  form  hydro- 
chloric acid,  and  the  oxygen  is  set  free.  Chlorin  in 
the  presence  of  water  acts  then  as  an  oxidizing 
agent,  for  the  oxygen  set  free  acts  upon  other  sub- 
stances present. 

OTHER  REACTIONS  OF -CHLORIN.  Chlorin  acts  upon  a 
large  number  of  hydrocarbons.  Thus,  methane  reacts 
with  chlorin  to  form  methane  chlorid,  more  commonly 
called  methyl  chlorid  or  chlor-methane : 

CH4  +  C12  — >  HC1  +  CH3C1 

Chlor-methane,  when  acted  on  afresh  by  chlorin,  gives 
di-chlor-methane,  CH2C12,  thus: 

CH3C1  +  C12-»CH2C12  +  HC1 

Similarly,  tri-chlor-methane,  CHC13,  commonly  called 
chloroform,  and  tetra-chlor-methane,  CC14,  may  be 
formed  by  the  further  action  of  chlorin.  Such  reac- 
tions as  these  where  one  element  is  substituted  for 
another  are  very  common  among  the  compounds  of 
carbon,  and  are  called  substitution  reactions. 

BLEACHING.  Most  textile  fabrics,  such  as  linen  and 
cotton,  naturally  have  a  yellow  tinge,  and  the  object  of 


172  Elementary  Chemistry 

bleaching  is  to  remove  this  color.  Formerly  the  fabrics 
were  spread  out  on  the  grass  and  kept  moist.  The 
oxygen  given  off  by  the  grass  which,  like  all  green 
plants  under  the  action  of  sunlight,  absorbs  carbon 
dioxid  and  gives  off  oxygen,  bleached  the  cloths.  This 
process,  although  effectual,  is  slow  anrd  expensive. 
Hence,  soon  after  the  discovery  of  chlorin  and  its  prop- 
erties, it  was  applied  in  bleaching.  Gaseous  chlorin, 
however,  is  not  ordinarily  used  because  of  the  difficulty 
of  manipulating  it,  but  a  solid  compound  which,  under 
proper  conditions,  readily  gives  off  chlorin,  is  used 
instead.  The  commonest  of  these  compounds  is  bleach- 
ing powder,  made  from  slaked  lime  and  chlorin.  It  is 
really  not  the  chlorin  which  does  the  bleaching,  but  the 
oxygen  which  the  chlorin  liberates  from  water.  This 
we  know,  because  dry  chlorin  will  not  bleach  at  all. 
Bleaching  is,  therefore,  a  process  of  oxidation,  the  prod- 
ucts of  which  are  colorless.  In  this  bleaching,  chlorin 
soon  attacks  and  destroys  the  fiber  of  the  cloth.  For 
this  reason  it  is  not  in  favor  among  laundresses  ;  they 
prefer  to  mask  the  yellowness  of  the  washed  cloth  by 
the  addition  of  "bluing,"  since  blue  and  yellow,  being 
complementary  colors,  appear  white  when  mixed. 
Manufacturers,  to  counteract  the  injurious  action  of 
chlorin  after  the  bleaching  is  accomplished,  use  cer- 
tain substances  called  "antichlors,"  which  form  harm- 
less compounds  with  the  excess  of  the  chlorin. 

LIQUID  CHLORIN.  When  a  solution  of  chlorin  in 
water  is  cooled  or  chlorin  is  passed  into  ice-cold  water, 
yellow  crystals  are  formed,  which  have  a  composition 
corresponding  to  the  formula,  C12  •  10  H2O.  This  chlorin 
hydrate  breaks  up  into  chlorin  and  water  when  heated, 
and  Faraday  made  use  of  this  compound  in  first  lique- 
fying the  element  in  1823,  according  to  the  method 
described  under  Ammonia  (page  65). 

Liquid  chlorin  is  bright  yellow,  and  solidifies  at 
temperatures  below -102°.  It  is  used  commercially  and 
is  stored  and  shipped  in  steel  cylinders  lined  with  lead. 

190.  Uses.  Chlorin  is  used  in  making  bleach- 
ing powder,  chlorates,  chloroform,  and  also  in  gold 
mining. 


The  Halogens  173 

FLUORIN 

191.  Preparation  and  Properties.     It  had  long 
been  suspected  that  certain  minerals  contained  an 
element  resembling  chlorin,  but  all  attempts  to  iso- 
late it  had  failed  until  Moissan  in  1886  subjected 
its  hydrogen  compound,  hydrofluoric  acid,  HF,  to 
electrolysis  conducted  at  low  temperatures  in  plati- 
num vessels.     Fluorin  is   a   lemon-colored  gas  of 
very   penetrating    and    disagreeable   odor.      It   is 
extremely  active  chemically,  combining  with  most 
other   elements ;   oxygen   is   a   notable    exception. 
It    decomposes    water    instantly,   forming    hydro- 
fluoric acid,  HF,  and  oxygen  mixed  with  ozone. 

BROMIN 

HISTORICAL  NOTE.  Bromin  was  discovered  in  1826 
by  Balard,  who  treated  the  liquor  left  after  the  crystalliz- 
ing of  the  common  salt  from  a  salt  spring  with  a  mixture 
of  manganese  dioxid  and  strong  sulfuric'acid.  He  gave 
it  the  name  of  bromin,  derived  from  the  Greek  word 
for  stench. 

192.  Occurrence.      Bromin   never   occurs   free, 
but  its  compounds  with  sodium,  potassium,  mag- 
nesium, and  several   other  metals   occur  in   small 
amounts  in  sea  water  and  some  mineral  springs. 
Small  quantities  of  silver  bromid,  AgBr,  occur  in 
some  Mexican  mines,  and  bromids  in  minute  pro- 
portion  are  found  in  connection  with  Chile  salt- 
peter, NaNOj. 

193.  Preparation.     Bromin  is  freed  from  com- 
bination either  by  heating  bromids  with  sulfuric 
acid   and  manganese   dioxid,   or  by  decomposing 
them  with  free  chlorin.     In  both  methods  the  sea 
or  salt  spring  water  is  first  concentrated  so  that  the 


1/4  Elementary  Chemistry 

chlorids  which  are  also  present  and  are  less  soluble 
than  the  bromids  may  crystallize  out.  The  crystals 
are  removed  from  the  residual  liquor  or  "mother 
liquor,"  which  is  named  "  bittern."  In  the  continu- 
ous process  the  hot  bittern  is  allowed  to  trickle  down 
through  a  tall  tower  filled  with  clay  balls  so  as  to 
meet  an  ascending  current  of  chlorin  gas  which  sets 
the  bromin  free  and  itself  combines  with  the  metals. 
The  bromin  dissolves  in  the  solution  and  is  collected 
in  a  cistern  at  the  base  of  the  tower.  In  the  periodic 
process  a  stoneware  still  is  charged  with  bittern, 
manganese  dioxid,  and  sulfuric  acid.  This  mixture 
is  heated  by  steam  and  the  bromin  which  is  given 
off  is  condensed. 

194.  Properties.    Physical.   (Table  L,  Appendix 
D.)     Bromin  is  a  dark  red,  volatile  liquid  of  strong 
and  disagreeable   smell ;    it  has   a   very  irritating 
action  on  the  eyes.     It  is  about  three  times  as  heavy 
as  water,  a  liter  of  which  dissolves  about  thirty-five 
grams. 

Chemical.  Bromin  combines  with  nearly  all  the 
elements ;  oxygen  is  the  chief  exception.  Its  action 
toward  metals  is  like  that  of  chlorin,  but  less  intense. 
A  mixture  of  bromin  vapor  and  hydrogen  has  to  be 
heated  to  cause  combination.  Bromin  decomposes 
water  slowly,  even  in  darkness,  and  hence  may  act 
as  an  oxidizing  agent  in  a  fashion  similar  to  chlorin. 
Water  and  bromin,  when  cold,  form  bromin  hydrate, 
Br2  •  ioH2O,  similar  to  chlorin  hydrate. 

195.  Uses.     Bromin  is  employed  in  the  manu- 
facture of  anilin  colors,  and  of  certain  of  its  salts. 
Silver  bromid  is  a   constituent  of  many  kinds  of 
photographic  plates  and  paper. 


The  Halogens  175 

IODIN 

HISTORICAL  NOTE.  The  ashes  of  some  seaweeds, 
called  kelp,  were  formerly  employed  in  making  sodium 
carbonate  (washing  soda),  and  Courtois,  in  1811,  on 
examining  the  mother  liquor  from  which  the  carbonate 
had  crystallized,  discovered  a  new  substance  which  he 
turned  over  to  Gay-Lussac  for  investigation.  Davy 
also  examined  the  same  substance  at  about  the  same 
time.  They  both  proved  it  to  be  a  new  element,  and  it 
was  given  the  name  of  "iodin"  (the  Greek  word  for 
violet  color)  because  its  vapor  is  violet. 

196.  Occurrence.     Iodin   does  not  occur  free. 
Small  amounts  of  its  compounds  with  the  metals 
potassium  and  sodium  are   found   associated  with 
many  other  substances.     The  principal  sources  of 
these  iodids  are  kelp  and  Chile  saltpeter. 

197.  Preparation.     Sodium  iodid,  Nal,  is  sepa- 
rated from  Chile  saltpeter  and  purified  by  repeated 
crystallizations.     It  is  then  dissolved  and  a  current 
of  chlorin  gas  passed  into  the   solution.     Sodium 
chlorid  is  formed  and  the  iodin  precipitated  as  a 
black  powder.     Or  the  mother  liquor  from  kelp  is 
treated  with   chlorin   as   above,  or  gently  heated 
with  sulf  uric  acid,  with  the  addition  of  small  quanti- 
ties of  manganese  'dioxid  from  time  to  time  until 
all  the  iodin  is  liberated.     Just  enough  manganese 
dioxid  is  added  to  free  the  iodin;  an  excess  is  avoided, 
as  it  would  cause  the  liberation  of  the  bromin  in  the 
bromids  accompanying  the  iodids.   The  iodin  result- 
ing from  both  processes  is  purified  by  sublimation. 

198.  Properties.    Physical.    (Table  I.,  Appendix 
D.)  Iodin  is  a  heavy,  grayish-black  solid  with  metallic 
luster,  and  an  odor  resembling  that  of  bromin,  but 
less  penetrating.     It  vaporizes  slowly  at  ordinary 


176  Elementary  Chemistry 

temperatures,  and  when  heated  turns  into  a  vapor  of 
a  dark  violet  color.  It  stains  the  skin,  paper,  etc., 
brown.  It  is  but  slightly  soluble  in  water,  giving  a 
solution  brown  in  color,  but  it  is  quite  soluble  in 
ether  and  carbon  bisulfid,  yielding  violet  solutions. 
It  also  forms  a  colorless  solution  in  an  aqueous 
solution  of  potassium  iodid. 

Chemical.  lodin  combines  with  most  of  the  ele- 
ments forming  iodids ;  it  does  not  burn,  but  by  an 
indirect  method  maybe  made  to  combine  with  oxy- 
gen to  form  iodin  pentoxid,  1 2  O  s ,  a  white  powder.  It 
combines  very  vigorously  with  phosphorus.  Nitro- 
gen iodid,  NI3,  a  compound  of  iodin  and  nitrogen, 
explodes  at  the  slightest  shock,  even  at  the  touch  of 
a  feather. 

199.  Uses.      A   solution   of  iodin   in   alcohol, 
which  is  known  as  "tincture  of  iodin,"  is  used  as  an 
external  application  in  medicine.    Iodin  enters  into 
the  composition  of  iodoform,  a  surgical  dressing,  and 
large  amounts  of  the  element  are  used  in  making 
certain  anilin  dyes. 

COMPOUNDS  OF  THE  HALOGENS  WITH 
HYDROGEN;   THE  HYDRACIDS 

200.  In  General.     One  volume  of  each  of  the 
halogens,  when  in  the  state  of  vapor,  combines  with 
an  equal  volume  of  hydrogen  gas  to  give  two  vol- 
umes of  a  gaseous  compound : 

F2  or  C12  or  Br2  or  I2  +  H?  — » 

2  HF  or  2  HC1  or  2  HBr  or  2  HI 
When  dissolved  in  water  these  hydrogen  com- 
pounds form  strong  acids,  often  called  hydr acids ; 


The  Halogens  177 

their  individual  names  are  hydrofluoric  acid,  HF, 
hydrochloric  acid,  HC1,  hydrobromic  acid,  HBr,  and 
hydriodic  acid,  HI.  They  are  also  called,  when 
in  the  gaseous  state,  hydrogen  or  hydric  fluorid, 
chlorid,  bromid,  and  iodid,  respectively. 

The  physical  and  chemical  properties  of  these 
compounds  are  very  similar.  They  are  all  colorless 
gases  with  sharp,  suffocating  odor  and  acid  taste, 
and  are  very  soluble  in  water.  They  dissociate  into 
their  elements  at  high  temperatures. 

HYDROCHLORIC   ACID 

HISTORICAL  NOTE.  Hydrochloric  acid  was  known 
to  the  ancients,  who  prepared  it  by  heating  a  mixture 
of  common  salt,  iron  pyrites,  and  clay.  Glauber,  in  the 
seventeenth  century,  substituted  oil  of  vitriol  for  the 
clay  and  pyrites,  but  it  was  not  until  the  end  of  the 
eighteenth  century  that  Cavendish  obtained  it  in  the 
gaseous  state  and  that  Priestley  studied  its  properties. 
It  was  formerly  called  "  spirits  of  salt  "  and  "  muriatic 
acid." 

201.  Occurrence.    Hydrochloric  acid  sometimes 
exists  in  volcanic  gases  and  is  occasionally  found 
in  rivers  whose  sources  are  in  volcanic  regions. 

202.  Preparation.     Common  salt  is  heated  with 
sulfuric    acid.      When    one    molecule    of    sodium 
chlorid  reacts  with  one  molecule  of  sulfuric  acid, 
only  one  hydrogen  atom  is  removed  from  the  mole- 
cule of  the  acid,  and  acid  or  hydrogen  sodium  sul- 
fate,  NaHSO4,  is  formed,  while  if  the  proportion  of 
salt  be  doubled,  normal  sodium  sulfate,  Na2SO4,is 
produced;   the  latter  reaction  occurs  at  a  higher 
temperature  than  the  former.      The  equations  are : 

NaCl  +  H2S04  ->     HC1  +  NaHSO4 
2  NaCl  +  H2SO4  — >  2  HC1  +  Na2SO4 


178  Elementary  Chemistry 

203.  Properties.     Physical.     The  aqueous  solu- 
tion of  hydrogen  chlorid  distils  at  110°;    the  dis- 
tillate contains  about  20  per  cent  of  HC1. 

Chemical.  Hydrogen  chlorid  does  not  support 
ordinary  combustion,  but  sodium  and  potassium,  if 
ignited  and  then  introduced  into  the  gas,  will  con- 
tinue to  burn  with  great  vigor ;  hydrogen  is  set  free 
and  chlorids  of  the  metals  are  formed.  Hydrogen 
chlorid  dissociates  at  high  temperatures,  and  electric 
sparks  effect  the  same  result  slowly. 

COMPOSITION.  If  a  given  volume  of  hydrogen  chlorid 
be  enclosed  in  a  tube  containing  a  little  sodium  or  alumi- 
num, and  the  metal  be  heated,  there  ensues  a  diminution 
of  one-half  in  volume,  and  the  residual  gas  is  hydrogen. 
Similarly,  if  a  little  manganese  dioxid  be  heated  in  a 
closed  tube  filled  with  hydrogen  chlorid,  there  is  a 
diminution  in  volume  amounting  to  one-half,  and  the 
gas  remaining  is  chlorin.  Hydrogen  chlorid  therefore 
consists  of  equal  volumes  of  hydrogen  and  chlorin. 

204.  Uses.     Hydrogen  chlorid  is  employed  in 
preparing  chlorin  by  Deacon's  process,  and  in  solu- 
tion for  the  same  purpose  in  Sche'ele's  and  Weldon's 
processes.     Hydrochloric  acid  is  used  in  medicine, 
and  in  the  manufacture  of  gelatin. 

HYDROFLUORIC  ACID 

HISTORICAL  NOTE.  The  fact  that  a  mixture  of  the 
mineral  fluorspar  (calcium  fluorid,  CaF2)  and  oil  of  vit- 
riol (sulfuric  acid),  when  gently  heated,  gives  off  vapors 
which  attack  glass,  was  known  and  utilized  in  the  etch- 
ing of  glass  in  the  seventeenth  century,  but  it  was  not 
until  1771  that  Scheele  succeeded  in  isolating  the  gas. 

205.  Preparation  and  Properties.    Calcium  fluo- 
rid is  pulverized  and  heated  with  strong  sulfuric 
acid,  best  in  a  leaden  vessel. 


The  Halogens  179 

CaF2  +  H2S04  ->  2HF  +  CaSO4 

Hydrogen  fluorid  combines  with  the  silicon  in 
glass  to  form  a  volatile  fluorid  of  silicon,  SiF4 .  As  it 
attacks  glass,  its  solution  has  to  be  stored  in  gutta- 
percha  or  lead  bottles.  This  property  of  attacking 
glass  is  utilized  in  the  manufacture  of  graduated 
glass  vessels,  such  as  burettes  and  pipettes. 

HYDROBROMIC  ACID 

206.  Preparation  and  Properties.  Hydrobro- 
mic  acid  cannot  be  prepared  by  the  action  of  concen- 
trated sulfuric  acid  on  a  metallic  bromid,  as  strong, 
hot  sulfuric  acid  decomposes  it.  If  the  acid  be 
diluted  with  about  a  third  its  volume  of  water,  how- 
ever, and  a  gentle  heat  applied,  hydrogen  bromid  is 
generated.  The  bromids  of  phosphorus  are  decom- 
posed by  water,  yielding  hydrobromic  acid.  A  cur- 
rent of  hydrogen  sulfid,  H2S,  when  passed  into  a 
solution  of  bromin  in  water,  is  decomposed  into 
sulfur  and  hydrogen ;  the  latter  unites  with  the 
bromin  to  give  a  solution  of  the  acid. 

H2S  +  Br2  — >2HBr  +  S 

A  very  convenient  method  consists  in  letting  bro- 
min fall  drop  by  drop  on  naphthalene  (moth  balls) 
contained  in  a  retort.  A  bromid  of  naphthalene  is 
formed  and  the  hydrogen  bromid  given  off  is 
absorbed  by  the  water. 

Hydrogen  bromid,  in  most  of  its  physical  and 
chemical  properties,  resembles  hydrogen  chlorid. 
It  is  a  colorless  gas  with  a  sharp  odor  and  a  very 
acid  taste.  It  is  extremely  soluble  in  water,  and 
the  solution  thus  formed,  if  saturated  with  the  gas, 


i8o  Elementary  Chemistry 

fumes  on  coming  in  contact  with  the  air.  Hydro- 
bromic  acid  attacks  most  metals  with  evolution  of 
hydrogen  and  formation  of  a  metallic  bromid. 

HYDRIODIC  ACID 

207.  Preparation  and  Properties.  Hydriodic 
acid  is  usually  prepared  by  the  action  of  water  on 
phosphorus  iodid  or  by  the  action  of  hydrogen  sulfid 
on  iodin  suspended  in  water. 

Hydriodic  acid  has  properties  similar  to  those 
of  the  other  hydracids.  It  is  decomposed  by  both 
bromin  and  chlorin,  which  combine  with  its  hydro- 
gen to  form  corresponding  hydracids,  and  set  the 
iodin  free.  Hydrogen  iodid  dissociates  at  about 
400°. 

OXYGEN  COMPOUNDS  OF  THE  HALOGENS 

No  oxids  or  oxygen-containing  acids  of  fluorin  are 
known.  Chlorin  forms  three  oxids:  chlorin  monoxid, 
C12O  ;  chlorin  dioxid,  C1O2  ;  and  chlorin  trioxid,  C12O3. 
They  are  all  heavy,  greenish  gases,  and  quite  unstable. 
Four  oxygen  acids  of  chlorin  are  known :  hypochlorous 
acid,  HC1O,  which  is  itself  unstable,  but  gives  certain 
important  salts,  as  calcium  hypochlorite,  CaCl2O2,  the 
active  constituent  of  bleaching  powder;  chlorous  acid, 
HC1O2,  which  may  be  prepared  by  dissolving  chlorin 
trioxid  in  water  ;  chloric  acid,  HC1O3,  which  is  a  strong 
oxidizing  agent  and  when  heated  breaks  up  into  oxygen 
and  perchloric  acid,  HC1O4. 

No  oxids  of  bromin  have  been  prepared,  but  the  two 
oxygen  acids,  hypobromous  acid,  HBrO,  and  bromic 
acid,  HBrO 3,  are  known. 

Two  oxids  of  iodin  exist :  iodin  tetroxid,  I2O4,  and 
pentoxid,  I2O5  ;  also  two  oxygen  acids  are  known  : 
iodic  acid,  H1O3,  and  periodic  acid,  HIO4.  All  four 
compounds  are  white  crystalline  solids  soluble  in  water. 


The  Halogens  181 

Exercises 

/.  How  can  chlorin  readily  be  distinguished  from  all  other 
gases  thus  far  studied  ? 

2.  What  are  the  chemical  reactions  involved  in  the  etching  of 
glass  ? 

j.  Of  the  properties  of  chlorin,  which  is  the  most  valuable 
commercially  ? 

4.  How  can  you  separate  iodin  from  sand  in  two  different 
ways  ? 

5.  Why  is  it  so  difficult  to  isolate  fluorin  ? 

6.  Write  the  equation  for  the  interaction  of  : 

(a)  H2S04,  MnO,,  KBr 
(£)  H2S04,  Mn02)  KI 

Problems 

1.  Chlorin  reacts  with  ammonia  according  to  the  equation  : 

8  NH3  +  3  CU  — >  6  NH4C1  +  N, 

How  many  liters  of  nitrogen  may  be  obtained  by  the  action  of 
chlorin  on  10 l-  of  ammonia?  How  many  liters  of  chlorin  will  be 
required  ? 

2.  If  the  weight  of  one  liter  of  hydrogen  chlorid,  HC1,  is  1.735^-, 
what  is  the  elemental  weight  of  chlorin  ? 

j.     How  much  potassium  is  needed  to  prepare  63.5  g-  of  iodin  ? 

4.  Hydrogen   and  chlorin   were  mixed   and  exploded  ;    the 
hydrogen  chlorid  produced  weighed  14.6  g-    What  were  the  weights 
and  volumes  of  the  hydrogen  and  chlorin  used  ? 

5.  How  many  grams  of  chlorin  can  be  obtained,  theoretically, 
by  the  electrolysis  of  100  g-  of  hydrochloric  acid  ? 

6.  How  many  grams  of  sodium  chlorid  are  required  to  prepare 
a  kilogram  of  hydrogen  chlorid  ? 

7.  A  room  6  m-  long,  5  m.  wide,  and  3.5  "*•  high  was  disin- 
fected with  chlorin  ;  enough  was  used  to  make. 0.15  per  cent  by 
volume  of  the  air  present.     How  man)''  grams  of  chlorin  were 
required  ? 

8.  How  many  liters  of  hydrogen  at  20°  and  773  mm.  can  be 
obtained  by  the  action  of  an  excess  of  zinc  upon  25. ®g-  of  hydro- 
chloric acid  ? 

g.  How  much  chlorin  can  be  obtained  from  the  oxidation  of 
1,000  ff-  of  hydrochloric  acid  ? 


1 82  Elementary  Chemistry 

jo.  Dumas,  in  1859,  heated  12.034^-  of  silver  bromid  in  an 
atmosphere  of  chlorin  and  obtained  9.185^-  of  silver  chlorid.  If 
the  atomic  weight  of  chlorin  is  35.45,  what  is  that  of  bromin  ? 

n.     The  analysis  of  a  certain  compound  gave  the  following 

results  : 

I  II  III 

C      =  12.00$  11.69$  H.83$ 

H    —    3.98$  4.02$  4.00$ 

N    =    6.77$  6.80$  6.78$ 

Br  =  77.s6$  77-6i$  77-64$ 
What  is  its  formula  ? 

12.  Marignac,  in  1843,  converted  100.000  parts  of  silver  into 
174.065  parts  of  silver  bromid.  The  atomic  weight  of  silver  is 
107.94  ;  what  is  that  of  bromin  ? 

7j.  Marignac,  in  1843,  heated  potassium  bromate,  KBrO3, 
and  obtained  71.277$  of  potassium  bromid,  KBr.  The  atomic 
weights  of  potassium  and  oxygen  are  39. 14  and  16.00,  respectively  ; 
what  is  that  of  bromin  ? 

14.  Ladenburg,  in  1902,  heated  63.8351  g-  of  silver  iodid  in  a 
current  of  chlorin  and  obtained  38. 9656^- of  silver  chlorid.  The 
atomic  weights  of  silver  and  chlorin  are  107.94  and  35.45,  respec- 
tively ;  what  is  the  atomic  weight  of  iodin  ? 

75*.  De  Luca,  in  1862,  by  repeatedly  evaporating  to  dryness 
2.667o<?".  of  fluorspar,  CaF2,  with  sulfuric  acid  obtained  4. 6590^-  of 
calcium  sulfate.  If  the  atomic  weights  of  calcium,  sulfur,  and 
oxygen  are  40.0,  32.06,  and  16.00,  respectively,  what  is  that  of 
fluorin  ? 

16.  The  specific  gravity  of  chlorin  referred  to  hydrogen  is 
nearly  36.  Compare  its  speed  of  diffusion  with  that  of  hydrogen. 

77.  If  hydrochloric  acid  contains  2.7  per  cent  of  hydrogen, 
how  many  liters  of  hydrogen  at  93°  and  265  mm-  can  be  obtained 
from  38^-  of  the  acid  ? 

18.  How  many  grams  of  manganese  dioxid  are  required  to 
prepare  loo.?"-  of  chlorin  from  hydrochloric  acid  ? 

ig.  A  saturated  solution  of  chlorin  when  exposed  to  sunlight 
yielded  20 c.c.  of  a  gas.  How  would  you  establish  the  identity  of 
this  gas,  and  how  much  chlorin  was  required  to  produce  it  ? 


CHAPTER  XVIII 


THE  ALKALI  METALS 

208.  In  General.  The  metals  lithium,  sodium, 
potassium,  rubidium,  and  ccesium  constitute  a  family 
of  very  similar  elements,  many  of  whose  compounds 
are  of  great  practical  importance.  They  are  all 
silvery-white  metals,  so  soft  as  to  be  easily  cut  with 
a  knife,  rapidly  tarnish  when  exposed  to  moist  air, 
decompose  water  at  ordinary  temperatures,  and 
burn  when  heated  in  the  air.  Their  salts,  with 
hardly  an  exception,  are  soluble  in  water.  Both 
their  physical  and  chemical  properties  vary  regu- 
larly with  their  atomic  weights  from  element  to 
element,  and  they  are  all  univalent. 


ELEMENT 

Symbol 

Atomic 
weight 

Density 

Melting- 
point 

Boiling 
point 

Lithium  

Li 

7.03 

0.59 

1  80° 

red  heat 

Sodium 

Na 

23.05 

0.974 

ex  6 

742° 

Potassium      

K 

39.15 

0.875 

62.5 

667 

Rubidium 

Rb 

8c  4. 

I   ^22 

18  S 

Caesium 

Cs 

\V\ 

I.8<5 

26.  ^ 

27O 

HISTORICAL  NOTE.  The  word  alkali  was  at  first 
applied  to  the  caustic  liquor  obtained  by  the  leaching 
of  wood  ashes,  and  to  distinguish  it  from  the  caustic 
liquor  containing  ammonium  carbonate  known  as  vola- 
tile alkali,  it  was  named  fixed  alkali.  Later  a  distinc- 
tion into  mineral  fixed  alkali  and  vegetable  fixed  alkali 
was  made,  as  it  was  believed  that  what  we  now  call 
caustic  soda  was  entirely  of  mineral  origin,  while  caustic 
potash  was  of  vegetable  origin.  The  fixed  alkalis  were 
held  to  be  elementary  in  nature,  but  Lavoisier  thought 


184  Elementary  CJicmistry 

that  "  these  substances  are  evidently  compounds, 
although  we  are  as  yet  ignorant  of  the  nature  of  the 
principles  entering  into  their  composition."  Davy  in 
1807  succeeded  in  isolating  potassium  and  sodium  by 
electrolysis  of  their  fused  hydroxids  ;  lithium  was  dis- 
covered in  1817,  and  rubidium  and  caesium  in  1860. 

209.  Lithium.      Lithium  is  widely  distributed, 
but  always  in  small  amounts.    It  is  prepared  by  the 
electrolysis  of  its  chlorid  either  fused  or  dissolved 
in  pyridin.     It  tinges  the  Bunsen  flame  crimson. 

SODIUM  AND  POTASSIUM 

210.  Occurrence.     Sodium  and  potassium  occur 
only  in  compounds.     United  with  oxygen,  silicon, 
and  aluminum,  they  are  found  in  especially  great 
abundance   in   feldspar   and  mica.      Common   salt 
(sodium  chlorid,  NaCl)  is  found  in  sea  water,  salt 
lakes,  or  as  the  mineral  rock  salt  or  halite.     Sea 
water  contains  about  3  per  cent  of  salt,  while  some 
salt  lakes  contain  as  much  as  30  per  cent,  so  that 
their  waters  are  nearly  saturated  with  it.     Sylvite 
(potassium  chlorid,  KC1)  and  carnallite,  KCl'MgCU, 
are  the  principal  minerals   containing  potassium. 
Potassium  nitrate  (niter  or  saltpeter),  KNO3,  was 
first   found    as   an   incrustation    in    certain    caves, 
whence  the  name  saltpeter  (salt  from  a  rock).    Chile 
saltpeter,  or  sodium  nitrate,  NaNO3,  forms  great 
beds  in  Chile.      Both  nitrates  are  formed  by  the 
action  of  .certain  microorganisms  on  decaying  ani- 
mal and  vegetable  matter. 

211.  Preparation.     Sodium  and  potassium  can 
be  obtained  by  electrolyzing  certain  of  their  com- 
pounds  either  in  solution    or  fusion.     They  may 
also  be  obtained  by  heating  their  hydroxids  with 


The  Alkali  Metals  185 

charcoal.  An  intimate  mixture  of  potassium  car- 
bonate and  charcoal  is  placed  in  a  retort  connected 
with  an  iron  receiver  from  which  the  air  is  excluded. 
At  a  high  temperature  the  carbonate  is  reduced 
with  formation  of  potassium  and  carbon  monoxid: 

K2CO3  +2C->2K  +  sCO 

The  metal  distils  over  into  the  receiver  and  is  col- 
lected under  petroleum.  Sodium  hydroxid  is  melted 
and  run  into  a  highly  heated  mass  of  coke  in  a 
retort : 

2  NaOH  +  C  ->  H20  +  CO  +  2  Na 

212.  Properties.  Physical.  (Table  I.,  Appendix 
D.)  Sodium  and  potassium  are  so  soft  that  they  can 
be  cut  easily  with  a  knife.  The  freshly  cut  surfaces 
have  a  bright  metallic  luster,  soon  tarnished,  how- 
ever, by  the  action  of  the  water  vapor  in  the  air. 
They  are  lighter  than  water. 

Chemical.  Both  sodium  and  potassium  combine 
eagerly  with  oxygen  and  many  other  elements. 
When  placed  upon  water  they  unite  with  a  portion 
of  it,  forming  the  hydroxids,  NaOH  and  KOH,  and 
setting  half  the  hydrogen  free.  So  much  heat  is 
liberated  that,  in  the  case  of  potassium,  the  escaping 
hydrogen  is  set  on  fire ;  with  sodium  this  occurs  only 
when  the  water  is  hot.  As  they  speedily  unite  with 
the  oxygen  and  water  vapor  of  the  air,  they  have  to 
be  protected  from  its  action  ;  this  is  usually  done  by 
keeping  them  under  naphtha  or  kerosene.  They 
are  very  energetic  reducing  agents,  and  unite  read- 
ily with  the  halogens.  Their  compounds  impart 
characteristic  colors  to  a  Buns-en  flame — potassium, 
violet,  and  sodium,  yellow. 


1 86  Elementary  Chemistry 

AMALGAMS.  The  alkali  metals,  when  placed  in  warm 
mercury,  dissolve  with  a  flash  of  light  and  the  evolution 
of  much  heat.  The  resulting  amalgams  are  liquid  when 
they  contain  less  than  5  per  cent  of  the  alkali  metal,  but 
are  dark  gray  solids  when  they  contain  more.  Many 
other  metals  also  form  amalgams  with  mercury,  but 
iron  and  platinum  are  notable  exceptions.  Amalgams 
are  not  true  compounds,  but  are  mixtures  or  solutions. 

213.  Ammonium.     The  radical,  NH4,  has  been 
found  to  form  compounds  similar  to  those  of  the 
alkali  metals.     The  radical   cannot,  indeed,  exist 
alone,  but  it  forms  an  amalgam  with  mercury. 

OXIDS  AND   HYDROXIDS  OF  THE  ALKALI   METALS 

214.  Oxids.    Sodium  and  potassium  burn  in  oxy- 
gen or  nitrous  oxid,  forming  several  oxids,  of  which 
the  most  important  are  the  per  oxids,  Na2O2    and 
KO2,  which  are  yellow  solids  reacting  with  water 
to  give  oxygen  and  the  respective  hydroxids.     At 
low  temperatures   and   with   an   excess   of   water, 
hydrogen  dioxid  is  also  formed. 

2Na2O2  +  2H2O-->4NaOH  +  O7 
Na2O,  +  2  H2O  ->  2  NaOH  +  H*7O2 
K204  +2H20->2KOH    +H202+02 

HYDROXIDS 

215.  Preparation.     Both  sodium  and  potassium 
hydroxids  were  formerly  made  by  the   action  of 
slaked  lime  (calcium  hydroxid,  Ca(OH)2)  on  solu- 
tions of  their  carbonates,  Na2CO3  and  K2CO3. 
Na2C03  or  K2CO3  +  Ca(OH), 

— >  2  NaOH  or  2  KOH  +  CaCO3 
The  insoluble  calcium  carbonate  is  removed  by 
filtration  and  the  solution  evaporated  to  dryness. 


The  Alkali  Metals  187 

The  resulting-  ''caustic  soda,"  or  "potash  by  lime," 
contains  impurities  which  are  insoluble  in  alcohol, 
and,  to  remove  them,  the  mass  is  treated  with  alco- 
hol. The  alcoholic  solution  is  filtered  off  and  evapo- 
rated first  in  iron  and  then  in  silver  vessels.  After 
the  alcohol  has  been  driven  off,  the  molten  alkali  is 
cast  in  silver  molds ;  the  product  is  known  as  "  soda  " 
or  "  potash  by  alcohol."  A  still  purer  grade  of  the 
alkalin  hydroxids  is  prepared  by  dissolving  the 
alkali  metals  in  water  and  evaporating  the  result- 
ing mixture  to  dryness. 

ELECTROLYTIC  PROCESSES.  In  the  Acker  Process 
melted  sodium  chlorid  is  electrolyzed  in  a  large  cast- 
iron  vessel ;  the  anode  consists  of  several  graphitized 
carbon  blocks  and  the  cathode  of  a  layer  of  molten  lead 
upon  which  the  sodium  chlorid  floats.  The  resistance 
which  the  electrolyte  offers  to  the  passage  of  the  current 
(which  is  very  strong)  changes  enough  of  the  electrical 
energy  into  heat  energy  to  keep  the  salt  at  a  tempera- 
ture about  75°  above  its  melting  point  (850°).  Chlorin 
which  is  evolved  at  the  anode  is  conducted  over  slaked 
lime,  with  which  it  reacts  to  form  chlorid  of  lime.  The 
sodium  forms  an  alloy  with  the  lead,  which  is  decomposed 
by  blowing  a  jet  of  steam  into  it,  whereby  caustic  soda 
and  hydrogen  are  formed  ;  the  latter  is  burned  as  soon 
as  evolved. 

In  Castner's  Process  a  solution  of  sodium  chlorid  is 
electrolyzed  in  an  ingeniously  devised  cell  in  which  the 
sodium  on  separating  out  forms  an  amalgam  with  some 
mercury  present  in  the  cell.  This  amalgam  is  automat- 
ically transferred  to  another  part  of  the  cell  containing 
iron  cathodes,  where  the  water  acts  upon  it ;  hydrogen 
is  set  free  with  the  formation  of  sodium  hydroxid. 

216.  Ammonium  Hydroxid.  Ammonium  hy- 
droxid is  made  by  dissolving  ammonia  in  water 
(§  73)-  When  boiled,  the  ammonia  escapes ;  hence 
it  is  sometimes  called  the  "volatile  alkali." 


1 88  Elementary  Chemistry 

217.  Properties  and  Uses.     Sodium  and  potas- 
sium hydroxids  are  white,  brittle  solids  of  disagree- 
able taste  and  are  very  soluble   in  water.     They 
absorb  carbon  dioxid  from  the  air,  forming  the  cor- 
responding carbonates,  and  are  very  deliquescent. 
They  are  powerful  solvents  of  animal  and  vegetable 
substances,  and  are  hence  said  to  be  "  caustic."  They 
are  used  in  immense  quantities  in  soap-making  and 
many  other  industries. 

218.  Ammonium   Hydroxid.      Ammonium    hy- 
droxid  resembles  solutions  of  sodium  and  potassium 
hydroxids,  but  is  not  nearly  so  caustic.     It  is  used  in 
the  laundry  and  for  cleansing  purposes  in  general. 

SOME  IMPORTANT  COMPOUNDS  OF  THE 
ALKALI  METALS 

HALIDS 

219.  Formation  of  Halids.     The  halogens  com- 
bine directly  with  the  alkali  metals  to  form  "halid 

salts":  2Na  +  Cl2  ->2NaCl 

The  halogen  acids  (hydracids)  react  with  the  alka- 
lin  hydroxids  in  aqueous  solution  : 

KOH  +  H'l -»  KI  +  H20 

Other  less  direct  methods  of  preparation  are  also 
employed. 

SODIUM   CHLORID 

220.  Salt  Making.     In  this  country  most  of  the 
table  salt  is  obtained  from  wells  bored  down  into 
salt  beds  lying  several  hundred  feet  below  the  sur- 
face of  the  ground.     The  salt  water  is  pumped  up 
and  evaporated  in  large  pans,  both  by  artificial  and 


The  Alkali  Metals  189 

the  sun's  heat.  The  crystals  which  at  first  separate 
out  consist  of  almost  pure  salt,  and  are  collected 
and  dried.  Sea  water  in  some  countries  is  dammed 
up  at  the  time  of  high  tide  in  immense  lagoons; 
the  water  is  allowed  to  evaporate  under  the  influ- 
ence of  the  sun's  rays,  and  the  crystals  which  form 
are  raked  out  Rock  salt  is  mined  in  many  parts  of 
the  globe,  and  is  purified  by  recrystallization. 

221.  Properties    and    Uses.      Sodium    chlorid 
forms  white  cubes  which  often  crystallize  in  beauti- 
ful hopper-like  aggregations.     Its  solubility  is  but 
slightly   affected   by   changes  of  temperature.     It 
is  not  deliquescent  when  perfectly  pure  ;  common 
table  salt  contains  a  trace  of  magnesium  chlorid, 
MgCl2,  which  is  very  deliquescent,  and  causes  the 
salt  to  stick  in  the  saltcellars  or  shakers  in  damp 
weather.     Besides  its  use  as  a  food  and  a  preserva- 
tive, salt  is  used  as  a  glaze  for  earthenware.     Salt 
is  necessary  for  the  preservation  of  animal  life,  for 
the  hydrochloric  acid  contained  in  the  gastric  juice 
of  the  stomach  is  derived  from  it.     It  is  the  source 
from  which  most  sodium  compounds  are  made. 

222.  Ammonium  Chlorid,  NH4C1.    Ammonium 
chlorid,  sometimes  called  sal  ammoniac,  is  obtained 
by  adding  hydrochloric  acid  to  the  ammonia  water 
obtained  in  the  manufacture  of  illuminating  gas: 

NH4OH  +  HC1  -»  NH4C1  +  H2O 

It  is  a  white  solid  with  a  sharp,  salty  taste,  and  is 
quite  soluble  in  water.  When  heated  it  sublimes, 
and  at  a  higher  temperature  dissociates  into  am- 
monia and  hydrogen  chlorid.  It  is  used  in  electric 
batteries  and  to  clean  metallic  surfaces  for  soldering. 


190  Elementary  Chemistry 

LAWS  OF  DISSOCIATION  ;  CHEMICAL  EQUILIBRIUM. 
Suppose  a  solid  A  to  dissociate  into  the  gases  B  and  C, 
and  let  a,  b,  and  c  denote  the  number  of  times  the 
formula  weight  (§  140)  of  each  substance  is  contained 
in  a  liter  of  the  mixture  of  the  three  substances.  It  has 
been  found  by  experiment  that  at  the  same  temperature, 
a /be  =  a  constant.  The  application  of  this  law  thus 
expressed  algebraically  may  be  illustrated  by  consider- 
ing the  dissociation  of  the  white  solid,  ammonium  chlo- 
rid.  This  when  heated  dissociates  into  the  two  gases, 
hydrogen  chlorid  and  ammonia.  Suppose  some  ammo- 
nium chlorid  to  be  placed  in  a  confined  vacuous  space 
(as  a  barometric  vacuum  of  one  liter's  capacity),  and 
heated  to  a  uniform  temperature.  A  definite  amount, 
«,  of  the  ammonium  chlorid  will  dissociate  into  the 
amounts  b  and  c  of  hydrogen  chlorid  and  ammonia, 
respectively,  and,  as  above,  a/  be  =  a  constant.  Sup- 
pose now  that  some  ammonia  be  introduced  into  the 
space  and  the  pressure  increased  so  as  to  keep  the 
volume  the  same.  The  value  of  c  is  thereby  increased, 
and  in  order  that  a /be  may  still  be  equal  to  a  constant, 
the  other  factor  in  the  denominator  must  decrease. 
Hence  enough  of  the  ammonia  added  will  combine  with 
some  of  the  hydrogen  chlorid,  forming  ammonium 
chlorid,  to  restore  the  equilibrium,  and  the  amount  of 
ammonium  chlorid  dissociated  is  diminished.  The  same 
effect  is  produced  by  adding  hydrogen  chlorid.  An 
excess  of  either  product  of  the  dissociation  diminishes 
the  amount  of  the  dissociation. 

MASS  ACTION  IN  ELECTROLYTES.  It  is  not  alone  the 
nature  of  reacting  substances  which  determines  how 
much  of  a  compound  can  be  formed,  but  also  the  rela- 
tive masses  of  the  reacting  substances.  Analogous 
facts  are  true  of  substances  undergoing  electrolytic 
dissociation.  To  diminish  the  dissociation  of  a  sub- 
stance in  solution  it  is  merely  necessary  to  add  to  the 
solution  another  substance  which  can  yield  one  or 
more  of  the  dissociation  products,  viz.,  ions  of  the  first 
substance.  And  an  excess  of  one  of  the  reacting  sub- 
stances will  accomplish  the  same  result  in  many  cases. 
Hence  the  practical  rule  of  adding  an  excess  of  the 
substance  which  is  to  precipitate  another  substance. 


The  Alkali  Metals  191 

SOLUBILITY  PRODUCT.  A  solution  is  said  t-o  be  sat- 
urated with  a  solute  at  a  given  temperature  when  the 
solute  ceases  to  dissolve.  A  state  of  equilibrium  then 
ensues  between  the  solute  and  the  solvent,  and  if  either 
is  changed  the  equilibrium  is  disturbed.  Thus,  a  solu- 
tion of  sodium  chlorid  contains  undissociated  molecules 

+ 

of  NaCl  as  well  as  the  ions  Na  and  Cl.  The  saturated 
solution  contains  all  the  chlorin  and  sodium  ions  it  can. 

If  hydrogen  chlorid,  HC1,  be  passed  into  such  a  saturated 

+ 

solution,  it  dissociates  partially  into  the  ions,  H  and  Cl. 
But  the  solution  is  already  saturated  with  chlorin  ions. 
Hence  some  of  them  are  thrown  out  of  solution,  and 
as  free  sodium  ions  cannot  exist  alone  in  a  solution,  an 
equal  number  of  them  is  precipitated  in  combination 
with  the  chlorin  ions,  so  that  solid  sodium  chlorid 
appears.  The  solution  keeps  saturated  with  chlorin 
ions,  while  the  number  of  sodium  ions  may  be  dimin- 
ished by  the  addition  of  hydrogen  chlorid.  Hydro- 
chloric acid,  therefore,  is  said  to  precipitate  sodium 
chlorid,  or  sodium  chlorid  is  less  soluble  in  hydrochloric 
acid  than  in  pure  water. 

If  ;;/,  r,  and  <r' represent  numbers  of  grams  of  sodium 
chlorid  molecules  and  of  sodium  and  chlorin  ions  equal 
respectively  to  their  molecular  or  atomic  weights  and 
contained  in  a  liter  of  saturated  solution,  the  equation 

c  x  c'  =  vi  X  a  constant 

has  been  proved  by  experiment  to  be  true.  Its  simi- 
larity to  the  equation  found  for  substances  undergoing 
ordinary  dissociation  is  apparent. 

223.     Potassium   Bromid,   KBr,   and   lodid,    KI. 

Potassium  bromid  and  iodid  are  prepared  by  adding 
bromin  or  iodin  to  a  solution  of  potassium  hydroxid 
until  the  solution  takes  on  a  yellowish  tinge.  Potas- 
sium bromid  (iodid)  and  bromate  (iodate)  are  thus 
formed : 

6KOH  +  6Br->sKBr  +  KBrO3  +  sH,O 
6KOH  +61    — >  5KI     +    KIO3    +  3H2O 


1 92  Elementary  Chemistry 

By  heating  the  potassium  bromate  (iodate)  it  is  con- 
verted into  potassium  bromid  (iodid)  and  oxygen. 
Potassium  bromid  and  iodid  are  white,  crystalline 
solids,  soluble  in  water.  Thev  are  used  in  medi- 
cine and  photography. 

224.  Ammonium  Sulfid,  (NH4)2S.     Ammonium 
sulfid  is  prepared  by  passing  hydrogen  sulfid  gas  into 
ammonium  hydroxid  to  saturation,  whereby  ammo- 
nium hydrosulfid,  NH4HS,  is  formed. 

NH4OH  +  H2S-»NH4HS  +  H2O 

and  then  adding  an  equal  bulk  of  the  ammonium 
hydroxid : 

NH4HS  +  NH4OH  — >  (NH4)2S  +  H2O 

When  freshly  prepared  it  is  a  colorless  liquid  of 
disagreeable  smell,  but  on  exposure  to  light  turns 
yellow  from  separation  of  sulfur. 

SODIUM  SULFATE  (Glauber's  Salt) 

225.  Preparation.    Sodium  sulfate,  also  known 
as  Glauber's  salt,  occurs  in  many  mineral  waters  and 
is  formed  in  the  manufacture  of  nitric  acid  when  sul- 
furic  acid  acts  upon  Chile  saltpeter.     It  is  also  pre- 
pared by  the  action  of  sulfuric  acid  on  sodium  car- 
bonate, the  first  step  in  the  manufacture  of  sodium 
carbonate  by  Le  Blanc's  process  (§  229).     Both  the 
acid    sulfate,    NaHSO4,   and    the    normal    sulfate, 
Na2SO4,  may  be  formed  in  this  reaction;  the  nor- 
mal salt  requires  the  higher  temperature : 

2NaCl  +  H2SO4      ->  HNaSO4  +  NaCl  +  HC1 
NaCl  +  HNaS04  ->  Na2SO4    +  HC1 

Common  salt  and   concentrated  sulfuric   acid  are 


The  Alkali  Metals  193 

heated  in  iron  or  lead  pans,  and  the  hydrogen  chlo- 
rid  is  absorbed  in  water.  When  the  formation  of 
the  acid  salt  is  completed,  it  is  raked  over  into  a 
reverberatory  furnace  (page  1 14),  where,  at  a  higher 
temperature,  it  is  converted  into  the  normal  salt. 

226.  Properties  and  Uses.    Sodium  sulfate  com- 
bines with  ten  molecules  of  water  of  crystallization, 
forming  a  glassy  solid,  Na2SO4-|-  ioH2O.   It  is  quite 
efflorescent,  falling  away  to  a  white  powder  when 
exposed  to  a  dry  atmosphere.     It  is  used  in  glass- 
making  and  medicine. 

227.  Potassium    Sulfate,    K2SO4.      Potassium 
sulfate  is  found  in  the  salt  deposits  at  Stassfurt.    It 
is  a  white,  crystalline,  soluble  solid  used  in  making 
alum  and  as  a  fertilizer. 

AMMONIUM  SULFATE,  (NH4)2SO4.  Ammonium  sul- 
fate is  made  by  adding  dilute  sulfuric  acid  to  ammonium 
hydroxid,  and  crystallizing  out  the  white  compound 
formed.  It  resembles  potassium  sulfate  and  is  used  for 
similar  purposes. 

SODIUM  CARBONATE,  Na2CO3  (Washing  Soda) 

228.  Sodium  compounds  seem  to  perform  the 
same  functions  in  the  economy  of  marine  plants 
that  the  corresponding  compounds  of  potassium  do 
in  land  plants.     The  ashes  of  marine  plants,  or  kelp, 
are  rich  in  sodium  compounds  and  were  formerly 
the  main  source  of  soda.     This  compound  is  now 
prepared  from  sodium  chlorid  or  from  cryolite. 

229.  Le  Blanc's  Process.    Sodium  sulfate,  called 
''salt  cake,"  is  heated  in   a  reverberatory  furnace 
with  coal  dust  and  powdered  chalk  or  limestone 
(calcium  carbonate).     After  the  mixture  has  melted 

it  is  raked  out  to  cool,  and  is  then  known  as  "ball 
u 


194  Elementary  Chemistry 

soda"  or  "  black  ash."  In  the  reaction  calcium  sulfid 
and  carbon  monoxid  are  formed  : 

Na2SO4  +CaCO3  +  40  — >  Na2CO3  +4CO  +  CaS 

The  carbonate  of  soda  is  washed  out  of  the  black 
ash,  and  the  solution  evaporated  to  dryness,  leaving 
"soda  ash,"  or  crude  carbonate  of  sodium. 

230.  Solvay's  Ammonia-Soda  Process.  Solvay's 
ammonia-soda  process  depends  upon  the  formation 
of  the  difficultly  soluble  acid  sodium  carbonate, 
NaHCO3,  when  an  ammoniacal  solution  of  sodium 
chlorid  is  saturated  with  carbon  dioxid : 

NaCl  +  NH3  +  H2O  +  CO2 

-^>NaHC03  +NH4C1 

The  acid  salt  is  filtered  off  and  converted  into  the 
normal  salt  by  heating : 

2  NaHCO3  ->  Na2C03  +  H2O  +  CO2 
The  carbon  dioxid  thus  regenerated  is  used  to  pre- 
cipitate fresh  amounts  of  the  acid  carbonate.     The 
ammonium  chlorid  obtained  is  heated  with  lime, 
and  the  ammonia  thus  regenerated : 
2  NH4C1  +  Ca(OH)2  ->  CaCl2  +  2  H2O  +  2  NH3 

SODIUM  CARBONATE  FROM  CRYOLITE.  Cryolite  is  a 
double  fluorid  of  sodium  and  aluminum  found  princi- 
pally in  Greenland.  When  heated  with  quicklime  it  is 
converted  into  insoluble  calcium  fluorid,  CaF2,  and 
sodium  ahiminate,  Na3AlO3  : 

Na3AlF6  +  3  CaO  — >  3  CaF2  +  Na3 A1O3 

The  calcium  fluorid  is  filtered  off  and  the  sodium  alumi- 
nate  treated  with  carbon  dioxid,  whereby  sodium  car- 
bonate and  insoluble  aluminum  hydroxid,  A1(OH)3, 
are  obtained : 

2  Na3A103  +  3  H20  +  3CO2 

*3Na2C03  +  2A1(OH)3 


The  Alkali  Metals  195 

231.  Properties  and  Uses.     Sodium  carbonate 
crystallizes  with  ten  molecules  of  water,  forming  a 
glassy,  efflorescent  solid,  commonly  called  sal  soda 
or  washing  soda.     It  has  an  alkalin  taste  and  is  very 
soluble.     It  is  extensively  used  in  the  laundry  and 
in  glass  and  soap  making. 

232.  Sodium  Bicarbonate  (Primary  or  Acid  Sodi- 
um Carbonate),  NaHCO3.    Sodium  carbonate  is  made 
by  passing  carbon  dioxid  into  a  solution  of  sodium 
carbonate  and  is  a  by-product  in  the  ammonia-soda 
process  (§230).      It,  as  well  as  the  corresponding 
potassium  compound,  HKCO3,  is  known  as  saleratus. 
When  heated  it  is  converted  into  the  normal  car- 
bonates : 

2NaHCO3  -»  Na2CO3  +  H2O  +  CO2 
It  forms  a  white  powder  which  is  soluble  in  water. 

BAKING  POWDERS.  Baking  powders  consist  of  sodium 
bicarbonate  mixed  with  some  acidifying  agent  as  potas- 
sium bitartrate  (cream  of  tartar),  KH(C4H4O6),  acid 
calcium  phosphate,  CaH4(PO4),  or  alum,  K2A12(SO4)4. 
A  "filling"  of  starch  or  flour  is  incorporated  so  as  to 
prevent  any  action  as  long  as  the  powder  is  kept  dry. 
When  water  is  added  to  it,  the  acid  liberates  the  carbon 
dioxid  in  the  bicarbonate,  and  when  the  latter  is  mixed 
with  dough,  the  dough  is  puffed  up  and  becomes  filled 
with  little  cavities  containing  carbon  dioxid,  or,  in  other 
words,  the  dough  "rises."  The  wholesomeness  of  a 
baking  powder  depends  not  only  upon  the  nature  of  the 
solid  products,  but  also  upon  the  care  exercised  in  the 
selection  of  pure  ingredients  and  in  mixing  them  in 
just  the  right  proportions. 

233.  Potassium  Carbonate,  K 2 CO 3.    Potassium 
carbonate  is  prepared  by  leaching  wood  ashes  and 
evaporating  the  solution  to  dryness  in  iron  pots. 
The  residue  is   called  potash,  and,  when   calcined, 


196  Elementary  Chemistry 

pearl  ash.  It  is  also  manufactured  from  potassium 
chlorid,  KC1,  by  both  the  Le  Blanc  and  Solvay  pro- 
cesses. It  is  a  white,  deliquescent  compound,  very 
soluble  in  water,  and  is  used  in  the  manufacture  of 
soft  soap  and  of  glass. 

234.  Potassium  Nitrate,  KNO3.  Potassium 
nitrate,  also  called  niter  and  saltpeter,  occurs  in  the 
juices  of  many  plants  and  is  found  in  the  soil  in 
considerable  amounts  in  certain  places  in  the  East 
Indies.  It  may  be  prepared  by  heaping  up  animal 
and  vegetable  refuse  matter  with  lime,  wood  ashes, 
and  soil,  and  keeping  the  mixture  exposed  to  the 
air.  A  microorganism  flourishes  under  such  con- 
ditions, and  slowly  brings  about  the  formation  of 
niter,  which  may  be  leached  out  and  purified  by 
crystallization.  The  natural  beds  of  Chile  saltpeter 
or  sodium  nitrate  were  probably  formed  in  somewhat 
the  same  manner. 

Burning  charcoal  deflagrates  when  thrown  on 
niter.  Paper  soaked  in  niter  solution  and  dried 
burns  slowly  and  steadily,  and  is  used  for  fuses 
under  the  name  of  touch-paper.  Potassium  nitrate 
has  a  cooling  taste,  and  is  used  as  a  remedy  for  sore 
throat  under  the  name,  sal-prunelle.  It  is  extensively 
employed  in  preserving  meat  and  in  the  manufac- 
ture of  gunpowder. 

GUNPOWDER.  Gunpowder  is  a  mixture  of  about  75 
parts  of  potassium  nitrate,  15  of  charcoal,  and  10  of  sul- 
fur. These  proportions  vary  somewhat,  each  maker 
having  his  own  formula  for  each  kind  of  powder.  The 
niter  must  be  free  from  deliquescent  compounds,  such 
as  Chile  saltpeter,  else  the  powder  would  become  damp. 
The  charcoal  is  made  from  light  woods  so  as  to  catch 
fire  readily,  and  distilled  rather  than  sublimed  sulfur  is 


The  Alkali  Metals  197 

preferable.  The  three  ingredients  are  first  ground  and 
sifted  separately,  then  mixed  in  the  proper  proportions 
and  made  into  a  thick  paste  with  water.  This  paste  is 
subjected  to  immense  pressure  and  forms  what  is  known 
as  press-cake.  These  cakes  are  broken  up  into  grains 
which  are  sorted  according  to  size  in  a  series  of  sieves 
and  dried  in  a  steam  bath.  The  grains  are  polished  by 
placing  them  in  revolving  barrels  together  with  a  little 
graphite. 

The  explosive  power  of  gunpowder  is  due  to  the 
sudden  formation  of  a  large  volume  of  gas,  mainly  car- 
bon dioxid  and  nitrogen.  One  volume  of  the  powder 
gives  nearly  4,000  volumes  of  the  gases. 

235.  Potassium  Chlorate,    KC1O3.     Potassium 
chlorate  may  be  prepared  by  passing  chlorin  into  a 
hot,  concentrated  solution  of  potassium  hydroxid: 

6KOH  +  3C12  ->5KC1  +  KC103  +  sH2O 

It  is  made  more  economically  by  running  chlorin 
into  hot  milk  of  lime : 

6Ca(OH)2  +  6Cl2->Ca(ClO3)2  +  5CaCl2  +  6H2O 

and  then  having  the  calcium  chlorate  formed  react 
with  potassium  chlorid : 

Ca(ClO3)2  +  2  KC1  — >  CaCl2  +  2  KC1O3 

It  is  a  white,  crystalline  solid  which,  mixed  with 
sugar  and  compressed  in  tablets,  forms  the  chlorate 
of  potasJi  tablets  used  as  a  remedy  for  sore  throat. 
When  heated  it  decomposes  into  potassium  chlorid 
and  oxygen  (§  30).  It  is  employed  in  the  manufac- 
ture of  matches,  fireworks,  and  smokeless  powder. 

236.  Potassium  Cyanid,  KCN.     Potassium  cya- 
nid  is  formed  when  nitrogenous  substances  of  ani- 
mal origin,  as  hoofs,  hides,  or  wool,  are  heated  with 
potassium  carbonate.      It  is  a  white,  deliquescent 


•198  Elementary  Chemistry 

solid,  very  soluble  in  water,  and  is  exceedingly 
poisonous.  It  is  a  good  reducing  agent,  taking 
oxygen  from  many  compounds  to  form  potassium 
cyanate,  KCNO.  Silver  salts  are  soluble  in  its  solu- 
tion, and  it  is  extensively  used  in  the  plating  of 
metals  by  electricity. 

RELATIONS  BETWEEN  THE  ATOMIC  WEIGHTS  OF  THE 
ALKALI  METALS.  A  comparison  of  the  atomic  weights 
of  lithium  (7),  sodium  .(23),  and  potassium  (39)  shows 
that  the  sum  of  the  atomic  weights  of  lithium  and  potas- 
sium is  just  double  that  of  sodium  : 

7  +  39  =  23 

Likewise  the  atomic  weight  of  rubidium  (85)  is  nearly 
the  mean  of  those  of  potassium  (39)  and  caesium  (133)  : 

39+133-  86 

2 

Exercises 

1.  Add  the  atomic  weights  of  chlorin  and  iodin  and  divide 
their  sum  by  two.     How  does  this   average   compare  with  the 
atomic  weight  of  bromin  ? 

2.  How    would    you    distinguish    ammonium    chlorid    from 
sodium  chlorid  ? 

j>.  How  would  you  test  a  washing  powder  for  an  ammonium 
compound  ? 

4.  What  are  the  chief  differences  between  ammonium  and 
ammonia  ? 

j.  How  do  (a)  ammonium  chlorid  and  (b}  ammonium  nitrate 
behave  when  heated  ? 

6.  How  may  the  existence  of  t>otassium  compounds  in  plants 
be  proved  ? 

7.  Why  does  the  electrolysis  of  an  aqueous  solution  of  sodium 
chlorid  give  sodium  hydroxid  and  hydrogen  at  the  cathode  ? 

8.  Which  of  the  following  gases  would  you  dry  with  solid 
caustic  potash  :     Ammonia,  carbon  monoxid,  carbon  dioxid,  oxy- 
gen? 


The  Alkali  Metals  199 

Problems 

1.  What  is  the  percentage  of  potassium  in   (a)  potassium 
bromid,  KBr,  (b)  potassium  nitrate,  KNO3  ? 

2.  10^-  of  gunpowder,   when   exploded,  yielded  3^-  of  gas 
measured  at  o°  and  760  mm.     What  would  be  the  volume  at  i, 800°, 
and  what  would  be  the  pressure  exerted  if  the  volume  was  kept 
unchanged  ? 

j.  Diehl,  in  1862,  obtained  from  15. 5  533<r-  of  lithium  carbon- 
ate, Li2CO3,  by  dissolving  it  in  sulfuric  acid,  9.24i4<r-  of  carbon 
dioxid.  Calculate  the  atomic  weight  of  lithium  on  the  basis  that 
the  atomic  weights  of  carbon  and  oxygen  are  12.0  and  16.0, 
respectively. 

4.  Dumas,   in   1859,  by  adding  silver  nitrate  to   a   solution 
containing  28. 7875^-  of  sodium  chlorid,  obtained  a  precipitate  of 
silver  chlorid  containing  53.1375  £•  of  silver.     What  is  the  atomic 
weight  of  sodium,  if  the  atomic  weights  of  silver  and  chlorin  are 
107.94  and  35-45.  respectively? 

5.  Penny,    in   1839,    changed  404.186^-   of    sodium  chlorate, 
NaClO3,  into  222.oi6<?"-  of  sodium  chlorid  by  heating  the  chlorate 
with  hydrochloric  acid.      The  atomic  weights  of  chlorin  and  of 
oxygen  are  35.45  and  16.00  ;  what  is  the  atomic  weight  of  sodium? 

6.  How  much  potassium  is  required  to  decompose  enough 
water  to  yield  226^-  of  hydrogen  at  20°  and  742  mm.  ? 

7.  What  is  the  percentage  of  water  crystallization  in  Glauber's 
salt,  Na2SO4+  10  H2O,  and  how  does  its  volume  in  the  free  state 
compare  with  its  volume  when  combined  with  the  salt,  if 

of  Na2SO4occupy37.7^-and  ioo&  of  Na2SO4  +  ioH8O,69.5*. 


CHAPTER   XIX 

EQUIVALENTS;  MOLECULAR  AND  ATOMIC 
WEIGHTS 

237.  Equivalent  Weights.  The  alkali  metals, 
sodium,  and  potassium,  decompose  water  with  evo- 
lution of  hydrogen,  and  it  has  been  found  that  23 £• 
of  sodium  and  39^-  of  potassium  are  required  to 
separate  out  from  the  water  i  s-  of  hydrogen.  Cer- 
tain other  metals,  such  as  magnesium,  iron,  zinc,  and 
aluminum,  dissolve  in  acids  with  evolution  of  hy- 
drogen ;  i  8-  of  hydrogen  is  liberated  by  12  #•  of  mag- 
nesium, 28^-  of  iron,  3 2. 5^- of  zinc,  or  9^-  of  aluminum. 
The  weights  of  metals  required  to  displace  the  unit 
weight  of  hydrogen  are  definite  and  are  called  the 
equivalent  zu  eights. 

Although  but  relatively  few  elements  displace 
hydrogen  from  water  or  acids,  the  conception  of 
equivalent  weights  may  yet  be  applied  to  all  the 
elements.  Thus,  the  analysis  of  water  proves  it  to 
contain  8  parts  by  weight  of  oxygen  and  i  part  of 
hydrogen.  The  equivalent  weight  of  oxygen  is 
therefore  8.  Now  oxygen  combines  with  most  other 
elements  so  that  the  analysis  of  their  oxids  will 
permit  us  to  determine  their  equivalent  weights. 
Thus,  magnesium  oxid  contains  12  parts  of  mag- 
nesium and  8  parts  of  oxygen.  Hence  the  equiva- 
lent weight  of  magnesium  is  12.  Similarly,  23^-  of 
sodium,  32.5^-  of  zinc,  and  28^-  of  iron  each  unite 
with  8^-  of  oxygen,  and  the  equivalents  found  by 
direct  comparison  with  hydrogen  are  confirmed. 

[200] 


Equivalents;  Molecular  and  Atomic  Weights     201 

Zinc,  magnesium,  and  some  other  metals,  when 
placed  in  a  solution  of  copper  sulfate,  dissolve, 
while  the  copper  separates  out  in  the  metallic  form. 
The  ratio  of  the  weight  of  the  metal  dissolved  to 
that  of  the  copper  precipitated  is  that  of  their 
equivalents.  Silver  neither  displaces  hydrogen 
nor  combines  readily  with  oxygen,  but  its  equiva- 
lent can  be  found  by  precipitating  it  from  solution 
by  means  of  zinc  or  some  other  metal.  It  is  possi- 
ble in  the  case  of  every  element  to  find  some  other 
element  with  which  it  may  react  in  such  a  way  that 
its  equivalent  may  be  determined. 

To  determine  the  equivalent  of  an  element, 
then,  it  is  necessary  to  find  by  experiment  what 
weight  of  the  element  combines  with  i  #-  of  hydro- 
gen or  takes  the  place  of  i  *"•  of  hydrogen  in  a  com- 
pound. If  this  is  impracticable,  w*e  must  ascertain 
the  weight  of  it,  which  combines  with  or  takes  the 
place  of  8^-  (more  exactly,  7.94 *"•)  of  oxygen,  or  the 
equivalent  weight  of  any  other  element. 

238.  System  of  Equivalents.  A  number  may 
thus  be  found  which  represents  a  definite  weight 
of  each  element  and  which  is  chemically  equiva- 
lent to  the  unit  weight  of  hydrogen.  The  system 
of  equivalents  is  based  on  experiment  alone,  and 
would  be  very  simple  and  convenient  if  it  were  not 
for  the  fact  that  certain  elements  have  more  than 
one  equivalent.  For  example,  copper  forms  two 
oxids,  one  red  and  the  other  black.  From  an  anal- 
ysis of  the  black  oxid  the  equivalent  of  copper  is 
31.5,  while  from  an  analysis  of  the  red  oxid,  its 
equivalent  is  just  twice  31.5  or  63.  Now  there  is 
no  way  of  deciding  on  experimental  evidence  alone 


2O2  Elementary  Chemistry 

which  equivalent  of  an  element  is  to  be  adopted, 
and  a  system  of  combining  numbers  based  on 
equivalents  alone  would  be  quite  arbitrary  and 
would  give  rise  (as  it  actually  did)  to  endless  con- 
troversy as  to  which  equivalents  should  be  chosen. 

239.  Electro-chemical  Equivalents.    If  the  same 
current  of  electricity  be  sent  through  a  solution  of 
a  silver,  a  zinc,  or  an  iron  salt  and  any  number  of 
acids,  the  continued  ratio  of  the  weights  of  silver, 
zinc,  or  iron,  and  hydrogen  thrown  out  of  solution 
will  be  1 08  :  32.5  :  28  :  i ;  that  is,  the  ratio  will  be  that 
of  the  chemical  equivalents  of  the  elements.     Fara- 
day discovered  this  fact  and  deduced  therefrom  the 
law: 

Equal  electric  currents  liberate  in  equal  intervals  of 
time  quantities  of  elements  proportional  to  their  chemical 
equivalents. 

Just  as  certain  elements  have  two  or  more  chem- 
ical equivalents,  so  do  they  have  two  or  more 
electro-chemical  equivalents.  Also,  some  elements 
do  not  form  solutions  conducting  electricity,  so  that 
their  electro-chemical  equivalents  cannot  be  deter- 
mined directly. 

240.  Equivalent  Weights  of  Compounds.    The 
equivalent  of  any  acid  is  that  weight  of  it  which 
combines  with  one  equivalent  of  a  univalent  metal ; 
the  acid  contains  at  least  one  equivalent  of  hydrogen 
replaceable  by  a  univalent  metal.     Thus,  the  equiv- 
alent weight  of  nitric  acid,  HNO3,  is  63,  and  is  the 
same  as  its  formula  weight;  that  of  sulfuric  acid, 
H2SO4,  however,  is  49,  which  is  one-half  its  for- 
mula weight.     The  equivalent  of  any  base  is  that 
weight  of  it  which  neutralizes  one  equivalent  of  an 


Equivalents;  Molecular  and  Atomic  Weights     203 

acid.  Thus,  40^  of  sodium  hydroxid,  NaOH,  neu- 
tralizes 63^-  of  nitric  acid;  hence  the  equivalent 
weight  of  sodium  hydroxid  is  40,  which  is  also  its 
formula  weight.  The  equivalent  weight  of  the  salt, 
silver  nitrate,  AgNO3,  is  the  same  as  that  of  its  for- 
mula weight,  viz.,  170,  because  that  weight  exactly 
reacts  with  one  equivalent  of  hydrochloric  acid,  HC1. 
In  similar  fashion  the  equivalent  weights  of  all 
compounds  can  be  fixed.  Each  case  has  to  be  con- 
sidered by  itself.  Attention  will  be  called  to  the 
matter  in  studying  the  various  substances  in  the 
sequel. 

241.  Law  of  Equivalent  Proportions.     The  re- 
lationships just  set  forth  are  entirely  general  and 
true  of  all  substances.     They  have  led  to  the  estab- 
lishment of  the  Law  of  Equivalent  or  Reciprocal 
Proportions : 

The  weights  of  different  substances  combining  with  a 
fixed  weight  of  a  given  substance  are  either  the  same  as, 
or  stand  in  a  simple  integral  relation  to,  the  weights  of 
these  substances  which  combine  with  one  another. 

HISTORICAL  NOTE.  The  first  notions  of  the  facts 
covered  by  this  law  were  gained  towards  the  end  of  the 
eighteenth  century,  but  the  full  import  of  the  law  was 
not  recognized  until  chemists,  chief  among  whom  was 
Berzelius,  began  to  fix  these  equivalents  with  accuracy. 
The  system  of  equivalents  which  arose  through  their 
labors  involved  too  many  inconsistencies,  however,  and 
it  was  not  until  Avogadro's  Hypothesis  was  revived  by 
Cannizzaro  in  1858  and  the  Doctrine  of  Valence  was 
propounded  that  order  was  introduced. 

242.  Avogadro's  Hypothesis.     The  simple  rela- 
tionships between  the  volumes  of  combining  gases 
discovered  by  Gay-Lussac  in   1808  and  expressed 


204  Elementary  CJicmistry 

as  the  Law  of  Volumetric  Proportions  ( §  51)  led 
Avogadro  in  181 1  and  Ampere  in  1814  to  the  follow- 
ing hypothesis : 

Equal  volumes  of  all  gases,  at  the  same  temperature 
and  pressure,  contain  equal  numbers  of  molecules. 

The  value  of  this  hypothesis  was  not  recognized 
until  1858,  when  Cannizzaro  showed  what  an  excel- 
lent basis  it  afforded  for  the  fixing  of  molecular 
weights.  It  is  to  be  carefully  noted  that  Avogadro's 
hypothesis  refers  only  to  molecules  and  not  to 
atoms. 

243.  Determination  of  Molecular  Weights  by 
Means  of  Avogadro's  Hypothesis.  It  is  an  experi- 
mental fact  that  two  volumes  of  hydrogen  combine 
with  one  volume  of  oxygen  to  produce  two  volumes 
of  steam.  It  is  also  an  experimental  fact  that  one 
liter  of  hydrogen  or  oxygen  weighs  twice  as  much 
as  does  the  smallest  amount  of  these  gases  con- 
tained in  a  liter  of  any  of  their  gaseous  compounds ; 
hence  the  formulas  of  hydrogen  and  of  oxygen  in 
the  free  state  are  H2  and  O2,  respectively. 

In  terms  of  the  Atomic  Theory  we  say  that  a 
molecule  of  hydrogen  and  oxygen  is  made  up  of 
two  atoms,  and  that  their  atomic  weights  are  half 
their  molecular  weights.  The  equation  represent- 
ing the  formation  of  water  from  its  elements  is : 
2H2  +  O2  -»2H2O 

Suppose  now  that  a  certain  volume  of  oxygen 
contains  a  billion  molecules.  Then,  by  Avogadro's 
Hypothesis,  an  equal  volume  of  any  other  gas,  at 
the  same  temperature  and  pressure,  must  contain 
the  same  number  of  molecules.  The  equation  may 
then  be  read : 


Equivalents;  Alolccular  and  Atomic  Weights     205 

Two  billion  molecules  of  Jiydrogen  unite  with  one 
billion  molecules  of  oxygen  to  for  in, two  billion  molecules 
of  ivater  vapor. 

Dividing  both  members  of  the  equation  by  a  bil- 
lion, we  have : 

Two  molecules  of  hydrogen  unite  with  one  molecule  of 
oxygen  to  produce  two  molecules  of  water. 

But  the  weights  of  equal  volumes  of  oxygen  and 
hydrogen  are  to  each  other  as  32  :  2.  Hence  the 
weights  of  their  molecules  must  be  in  the  same 
ratio.  One  liter  of  water  vapor  weighs  0.805  8'  and 
one  liter  of  hydrogen  0.09^-  Hence  steam  weighs 

-  =  Q  (nearly)  times  as  much  as  the  same  vol- 

0.09 

ume  of  hydrogen,  /.  c.,  its  specific  gravity  is  9.  The 
weight  of  a  steam  molecule  is  therefore  9  times  that 
of  a  hydrogen  molecule,  or  9X2=18  times  that  of  a 
hydrogen  atom.  Since  the  specific  gravity  of  steam 
referred  to  hydrogen  is  9,  its  molecular  weight  is 
equal  to  twice  its  specific  gravity. 

If  then  we  adopt  Avogadro's  Hypothesis,  we  are 
in  a  position  to  find  molecular  weights  by  means  of 
vapor  density  determinations.  By  the  molecular 
weight  of  a  gas  we  understand  the  number  of  times 
heavier  its  molecule  is  than  the  weight  of  one  atom 
of  hydrogen.  Now  the  weight  of  one  atom  of  hydro- 
gen is  the  standard  in  the  determinations  of  molec- 
ular weights,  while  the  weight  of  one  molecule  of 
hydrogen  (equal  to  the  weight  of  tivo  atoms]  is  taken 
as  the  standard  in  density  determinations.  Hence: 

To  find  the  molecular  weight  of  a  gas,  double  its 
density  referred  to  hydrogen,  or  divide  the  weight  of  a 
liter  of  it  by  0.045,  the  elemental  weight  of  hydrogen. 


206  Elementary  CJiemistry 

•9 

244.  Determination  of  Atomic  Weights  by 
Means  of  Avogadro's  Hypothesis.  While  it  is  thus 
a  comparatively  simple  matter  to  fix  the  molecular 
weight  of  a  vaporizable  substance  by  Avogadro's 
Hypothesis,  atomic  weights  can  be  found  only  when 
the  number  of  atoms  in  a  molecule  of  an  element 
is  known.  All  the  gaseous  compounds  containing 
the  element  must  be  analyzed  and  their  molecular 
weights  found  by  vapor  density  determinations. 
The  results  are  compared  and  the  smallest  amount 
of  the  element  contained  in  a  molecule  of  any  of  its 
gaseous  compounds  chosen  as  its  atomic  weight. 
Thus,  of  the  almost  innumerable  compounds  of  car- 
bon which  have  been  investigated,  not  one  has  been 
found  to  contain  in  its  molecule  a  relative  weight  of 
less  than  12  for  carbon.  Hence,  12  is  taken  as  the 
atomic  weight  of  carbon. 

In  this  way  the  conclusion  has  been  reached  that 
most  elements  have  molecular  weights  which  are 
multiples  of  their  atomic  weights.  The  molecule 
of  hydrogen,  nitrogen,  and  oxygen  we  have  found 
to  consist  of  two  atoms  each,  and  several  other 
elementary  gases  have  a  similar  structure.  Certain 
other  elements,  such  as  phosphorus  and  sulfur,  have 
gaseous  molecules  that  are  made  up  of  more  than 
two  molecules,  while  still  others,  such  as  mercury 
and  zinc,  have  molecules  which  are  identical  with 
their  atoms. 

Molecular  weights  as  determined  by  means  of 
Avogadro's  Hypothesis  apply  to  gaseous  substances 
only,  and  may  be  different  when  the  substances  are 
in  the  liquid  or  the  solid  state.  The  special  methods 
which  have  been  devised  to  ascertain  the  molecular 


Equivalents;  Molecular  and  Atomic  Weights    207 

weights  of  liquids  and  solids  are  too  difficult  to  be 
discussed  here.  From  lack  of  more  definite  knowl- 
edge it  is  assumed  that  the  solid  and  liquid  mole- 
cules contain  the  same  number  of  atoms  as  they  do 
when  vaporized. 

245.  How  to  Find  the  Atomic  Weight  of  Nitro- 
gen. We  know  by  experiment  the  vapor  density 
and  the  composition  of  a  number  of  compounds  of 
nitrogen,  and  can  deduce  therefrom  their  molecular 
weights,  the  proportion  of  the  elements  in  each  com- 
pound and  its  formula.  In  the  following  table  are 
given  the  mass  and  volume  relationships  of  a  num- 
ber of  nitrogen  compounds. 


NAME 

Vapor 
density 

Molecu- 
lar 
weight 

Weight 

.°f 
nitrogen 

Weight 
of 
other 
elements 

Formula 

Ammonia  

8.5 

17 

14 

'i 

NH3 

Hydrazin 

16 

T.2 

2  X  14 

N  H 

Hydrazoic  acid 

22.5 

43 

3  X  14 

I 

NgH 

Cyanogen  

26 

52 

2  X   14 

24 

C,N, 

Nitrogen  monoxid  
Nitrogen  dioxid  

22 
15 

44 
30 

2  X   H 
14 

16 
16 

N20 
NO 

In  looking  down  the  column,  "  Weight  of  nitro- 
gen," we  see  that  14  is  the  smallest  weight  that 
occurs,  and  hence  conclude  that  14  is  the  atomic 
weight  of  nitrogen.  If,  however,  in  the  future 
some  other  compound  of  nitrogen  should  be  dis- 
covered in  which  the  weight  of  hydrogen  was 
found  to  be  less  than  14,  the  lesser  number  would 
have  to  be  taken  as  the  atomic  weight  of  nitrogen. 
It  is  apparent  that  we  can  never  be  quite  sure  that 
we  know  the  right  atomic  weight  of  an  element,  for 
compounds  may  yet  be  discovered  in  which  the 
atomic  weight  is  different  from  that  now  adopted. 


208 


Elementary  Chemistry 


246.  Equivalent  and  Atomic  Weights  Com- 
pared. In  the  following  table  are  given  the  equiva- 
lent and  atomic  weights  of  some  familiar  elements  ; 
their  valencies  are  marked  by  accents. 


J?  1  J^MfiNT^ 

Equivalent 

Atomic 

Atomic 
weight 

weight 

weight 

Equivalent 
weight 

Aluminum'"  .. 
Chlorin  '    .  .  .    .  .    
Copper  '  or  " 

9 
35-43 
63.6  or  31.8 

27.1 

35-43 
63  6 

3  (nearly) 
i 
i  or  2 

Iron 

28 

56 

2 

Magnesium  "              . 

12.2 

24.4 

Oxygen"  

Lead  " 

8 
103.46 

16 
206.92 

2 
2 

Potassium  ' 

39.  i 

39.1 

I 

Sodium  '            .             

23 

23 

I 

Tin"0"'".             

29.8  or  59.5 

119 

2  or  4 

Zinc"       .             

32.7 

65-4 

This  table  might  be  extended  to  cover  all  the 
elements,  but  enough  examples  are  given  to  illus- 
trate the  relationships.  There  has  always  been  a 
certain  arbitrariness  exercised  in  the  fixing  of 
equivalents;  those  given  are  such  as  may  be  deter- 
mined by  the  student  himself.  It  is  seen  that  the 
atomic  weights  are  never  less  than  the  equivalent 
weights  and  may  be  one,  two,  three,  or  four  times 
as  large.  It  may  not  be  amiss  to  reiterate  that  the 
numbers  representing  the  equivalents  denote  how 
many  times  heavier  the  element  is  than  the  weight 
of  hydrogen  to  which  it  is  equivalent,  while  the 
numbers  standing  for  the  atomic  weights  show  how 
much  heavier  the  atom  of  the  element  is  than  the 
atom  of  hydrogen. 

247.  Equivalents  and  Valence.  Reference  to 
the  table  just  given  shows  that  chlorin,  sodium,  and 
potassium  are  univalent  and  their  equivalent  and 


DUMAS 


GRAHAM 


STAS  HOFMANN 

Plate  1 


THOMAS  GRAHAM 
1805-1869  ;   English 

Discovered  laws  of  diffusion  of 
gases,  basicity  of  acids.  Con- 
tributed to  the  knowledge  of 
water  of  crystallization  and  of 
dialysis 


JEAN  BAPTISTE  ANDRE  DUMAS 

1800-1884;  French 

Fixed  many  atomic  weights. 
Ascertained  with  great  accuracy 
the  composition  of  water  and  air. 
Devised  method  ofjitiding  vapor 
densities 


AUGUST  WlLHELM  HOFMANN 
1818-1892  ;  German 

Active   in    domain    of   organic 
chemistry.      Discovered    impor- 
tant coal-tar  dyes 


JEAN  SERVAIS  STAS 
1813-1891  ;  Belgian 

Made   accurate   determinations 

of  the  atomic  weights  of  many 

elements 


Plate  V 


Equivalents;  Molecular  and  Atomic  Weights     209 

atomic  weights  are  the  same.  Iron,  magnesium, 
oxygen,  lead,  and  zinc  are  usually  bivalent,  and 
their  equivalents  are  half  their  atomic  weights. 
Aluminum  is  trivalent,  and  its  equivalent  is  one- 
third  its  atomic  weight.  Univalent  copper  has  its 
equivalent  and  atomic  weight  equal,  while  bivalent 
copper  has  an  atomic  weight  twice  that  of  its  equiv- 
alent. Bivalent  or  quadrivalent  tin  has  an  equivalent 
either  one-fourth  or  one-half  the  atomic  weight.  By 
comparing  all  the  elements  in  this  way  we  find  that : 

The  atomic  weight  of  an  element  is  equal  to  its  equiv- 
alent multiplied  by  its  valency. 

We  now  can  see  how  the  system  of  molecular 
and  atomic  weights  supplanted  that  of  equivalents. 
All  elements  were  at  first  supposed  to  have  the  same 
combining  power ;  they  were  equal-valued  or  equiva- 
lent. When  Avogadro's  Hypothesis  was  adopted, 
however,  it  became  evident  that  they  were  not 
equal-valued,  but  that  some  had  a  greater  combin- 
ing power  than  others.  From  this  conception  arose 
the  Doctrine  of  Valence.  The  system  of  equivalents 
was  based  on  mass-relationships.  With  Avogadro's 
Hypothesis  came  the  requirement  that  volume-rela- 
tionships should  also  be  considered,  and  that  the 
choice  of  molecular  weights  is  regulated  by  a  physi- 
cal property,  that  of  vapor  density. 

248.  Equivalents  and  Valence  of  Radicals. 
Radicals  as  well  as  elements  have  equivalents  and 
valence.  In  nitric  acid,  HNO3,  the  radical,  NO3,  is 
combined  with  one  atom  of  hydrogen,  and  it  is 
therefore  univalent.  The  radical,  SO4,  combines 
with  two  atoms  of  hydrogen  to  form  sulfuric  acid, 
H2SO4,  and  is  therefore  bivalent. 


2io  Elementary  Chemistry 

249.  Basicity  and  Acidity,  When  the  formula 
weight  and  the  equivalent  weight  of  an  acid  are  the 
same,  the  molecule  of  the  acid  contains  but  one 
hydrogen  atom  which  is  replaceable  by  a  univalent 
metallic  atom  or  radical  to  form  a  salt.  Such  an 
acid  is  said  to  be  monobasic.  Thus  nitric  acid,  HNO3 , 
is  monobasic,  and  forms  salts  of  the  type  M/NOj, 
where  M'  represents  any  univalent  metal  or  metal- 
like  radical.  Potassium  nitrate,  K/NO3,  and  ammo- 
nium nitrate,  (NH4)'NO3,  are  examples.  Hydro- 
chloric acid,  HC1,  and  acetic  acid,  H(C2H3O2),  are 
also  monobasic,  and  there  are  many  others. 

When  the  formula  weight  of  an  acid  is  twice  its 
equivalent  weight,  the  molecule  of  the  acid  contains 
two  hydrogen  atoms  which  are  replaceable  by  two 
univalent  metallic  atoms  or  radicals  or  by  one  biva- 
lent metallic  atom  or  radical.  Thus,  sulfuric  acid 
has  a  formula  weight  of  98  #•  and  an  equivalent 
weight  of  49^-  and  forms  salts  of  the  type  MXSO4, 
where  M'  is  univalent,  or  M;/SO4,  where  M"  is 
bivalent.  Sodium  sulfate,  Na2SO4,  and  calcium 
sulfate,  Cax/SO4,  are  examples. 

Likewise,  the  molecules  of  tribasic  acids  contain 
three  hydrogen  atoms  replaceable  by  (a)  three  uni- 
valent metallic  atoms  or  radicals,  (&)  one  univalent 
and  one  bivalent  metallic  atom  or  radical,  and  (c) 
one  trivalent  atom  or  radical.  Their  formula  weight 
is  three  times  their  equivalent  weight.  Thus,  phos- 
phoric acid,  H3PO4,  yields  the  salts,  tri-potassium 
phosphate,  K3PO4,  aluminum  phosphate,  A1PO4; 
but  no  salt  of  the  type  M//M/PO4  has  been  prepared. 

When  the  equivalent  and  formula  weights  of  a 
base  are  the  same,  the  molecule  of  the  base  contains 


Equivalents;  Molecular  and  Atomic  Weights     21 1 

one  hydroxyl  group  replaceable  by  the  univalent 
anion  of  an  acid.  Thus,  the  hydroxids  of  sodium 
and  potassium,  NaOH  and  KOH,  form  salts  of  the 
type  NaA'  and  KA',  where  A'  is  a  univalent  anion. 
Such  bases  are  said  to  be  monacidic. 

Likewise,  there  are  diacidic  bases,  such  as  calcium 
hydroxid,  Ca(OH)2,  and  boron  hydroxid,  and  tri- 
acidic  bases,  such  as  bismuth  hydroxid,  Bi(OH)3,  but 
bases  with  an  acidity  greater  than  three  are  not 
known  to  exist. 

250.  Acid  and  Basic  Salts.  Dibasic  acids  may 
form  two  series  of  salts.  In  one  but  half  of  the 
hydrogen  is  replaced  by  a  univalent  metal  or  radi- 
cal, while  in  the  others  all  of  the  hydrogen  is 
replaced.  Thus,  sulfuric  acid  forms  the  series  of 
salts  of  the  type  M'HSC^,  where  M'  is  a  univalent 
metal  or  radical,  and  also  the  series  M/SO4.  An 
example  of  the  first  series  is  hydrogen  sulfate  (also 
called  acid  sodium  sulfate),  NaHSO4;  an  example 
of  the  second  series  is  disodium  sulfate  or  normal 
sodium  sulfate  (usually  called,  simply,  sodium  sul- 
fate), Na2SO4. 

Tribasic  acids  in  like  manner  may  form  three 
series  of  salts,  since  their  hydrogen  is  replaceable 
in  three  stages. 

Salts  of  di-  and  tribasic  acids  still  containing  re- 
placeable hydrogen  are  called  acid  salts.  They  may 
usually  be  converted  into  normal  salts  when  enough 
of  the  base  is  added  to  replace  the  hydrogen.  Con- 
versely, normal  salts  are  converted  into  acid  salts 
by  treatment  with  more  of  the  acid. 

Usually  solutions  of  acid  salts  have  an  acid  reac- 
tion, but  if  they  are  composed  of  a  strong  base  and 


212  Elementary  Chemistry 

a  weak  acid,  the  reaction  may  be  alkalin,  as  is  the. 
case  with  disodium  hydrogen  phosphate,  Na2HPO4, 
and  sodium  hydrogen  carbonate  (ordinarily  known 
as  bicarbonate  of  soda),  NaHCO3. 

In  like  fashion  the  hydroxyl  groups  of  bases  con- 
taining a  bivalent  or  trivalent  metal  might  be  sub- 
stituted in  two  or  three  stages.  This  does  not  take 
place  in  the  case  of  the  common  bases,  however; 
that  of  bismuth  is  about  the  only  one  we  shall 
encounter. 

Problems 

/.  A  certain  gas  is  22  times  heavier  than  an  equal  volume  of 
hydrogen.  What  is  its  molecular  weight  ?  What  familiar  gas  has 
that  molecular  weight? 

2.  If  spc-c.  of  methane  contain  io20  molecules,  how  many 
molecules  will  100^-  of  acetylene  contain,  if  the  conditions  of  tem- 
perature and  pressure  are  the  same  for  both  gases  ? 

j.  A  piece  of  lithium  was  placed  on  water  ;  it  dissolved,  form- 
ing lithium  hydroxid,  LiOH,  and  evolved  656 c.c.  of  hydrogen  at 
21°  and  743  mm..  If  the  equivalent  of  this  metal  is  7,  what  was 
the  weight  of  the  lithium  taken  ? 

4.  The  weight  of  a  liter  of  ether  vapor  at  100°  and  760  mm.  is 
2. 44^-.     What  is  its  molecular  weight  ? 

5.  Lime,  CaO,  contains  71.43  per  cent  of  calcium  and  28.57 
per  cent  of  oxygen.     What  is  the  atomic  weight  of  calcium  ? 

6.  The  molecular  weight  of  bromin  is  160.     What  is  its  vapor 
density  referred  to  hydrogen  ? 

7.  If  a  liter  of  sulfur  dioxid  weighs  2.86<?"-,  what  is  its  molec- 
ular weight  ? 

8.  How  many  cubic  centimeters  of  carbon  monoxid  weigh 
I.884T-  ? 

9.  The  vapor  density  of  chlorin  is  35.45  ;  what  is  its  molec- 
ular weight  ? 

10.  3. 8o8<?"-  of  a  gas  occupies  2703. ^c.c.  at  15°  and  740^^-.    Find 
its  molecular  weight. 

11.  The  specific  gravity  of  mercuric  chlorid  referred  to  air  is 
9.8.     It  contains  73.93  per  cent  of  mercury  (Hg)  and  26.07  per  cent 
of  chlorin  (Cl).     What  then  is  the  formula  for  mercuric  chlorid  ? 


Equivalents;  Molecular  and  Atomic  Weights     213 

12.  Calculate  the  formulas  of  the  compounds  having  the  fol- 
lowing percentage  composition  and  vapor  density  : 

(a)  C  =  92. 3$  ;     H  =  7.7$  ;  vapor  density  =  39 

(b)  C  =  73.8$  ;     H  _-  8.7$  ;     N*^  17.5^  ;    vapor  density  =  80.2 

(c)  C  =  39.9$  ;     H  =  6.7$  ;     O  =  53.4$  ;    vapor  density  =  30.5 

(d)  C  =  10.04$  ;  H  =  0.84$  ;  Cl  =  89.12^  ;  vapor  density  =  59.7 
7j>.     If  (as  was  the  case  in  the  second  quarter  of  the  nineteenth 

century)  the  unit  of  comparison  were  O  =  100,  what  would  be  the 
equivalents  of  (a)  sodium,  (b}  hydrogen,  (c)  magnesium  ? 

14.  Gladstone  and  Hibbert,  on  passing  the  same  electric  cur- 
rent through  solutions  of  zinc  and  silver  solutions,  obtained  quan- 
tities of  the  metals  in  the  ratio  of  i  (Zn)  :  3.298  (Ag).  If  the 
equivalent  of  silver  is  107.94,  what  is  that  of  zinc  ? 

75.  What  is  the  equivalent  of  nickel  if  it  dissolves  in  acids 
with  the  evolution  of  a  mass  of  hydrogen  equal  to  3.411  per  cent 
of  its  own  mass  ?  What  is  its  atomic  weight  if  it  is  bivalent  ? 

16.  If  the  atomic  weight  of  silver  is  107.94  an(i  if  the  same 
electric  current,  on  passing  through  solutions  of  silver  and  copper 
salts,  precipitates  weights  of  the  metals  in  the  ratio  of  i  (Cu) : 
3.408  (Ag),  what  is  the  atomic  weight  of  copper  ? 

77.  If  copper  oxid,  heated  in  an  atmosphere  of  hydrogen, 
lost  59.7893^"-  of  oxygen  and  formed  67.2S25-?"-  of  water,  what  is 
the  atomic  weight  of  (a)  oxygen  referred  to  hydrogen  as  one,  and 
(b~)  hydrogen  referred  to  oxygen  as  sixteen  ? 

18.  If  -JSQC.C.  of  carbon  monoxid  weigh  0.94^"-,  what  is  the 
molecular  weight  of  the  compound  ? 

J~9-  45-73i-^-  of  silver  combine  with  chlorin  to  form  60. 7496  <?"• 
of  silver  chlorid,  AgCl,  If  the  equivalent  of  chlorin  is  35.45,  what 
is  that  of  silver  ? 

20.  If  a  certain  current  of  electricity  deposited  31.  -jg-  of  cop- 
per, how  much  (a)  silver,  (b)  zinc  would  it  deposit  ? 


CHAPTER  XX 

METHODS     OF     DETERMINING     MOLECU- 
LAR AND  ATOMIC  WEIGHTS 

251.  Vapor  Density.  When  a  chemist  has  pre- 
pared a  substance  which,  from  its  method  of  prepara- 
tion arid  its  properties,  he  has  reason  to  believe  has 
never  been  obtained  before,  he  analyzes  it  to  find 
out  the  proportions  in  which  its  constituent  ele- 
ments are  combined.  From  the  percentage  compo- 
sition (§  138)  he  can  deduce  a  formula,  which,  how- 
ever,, is  still  doubtful  (§  139)  unless  he  has  some 
means  of  finding  the  weight  of  a  liter  of  the  sub- 
stance in  gaseous  (or  dissolved,  cf.  below)  form. 
From  the  weight  of  a  liter  of  the  vapor  he  can 
readily  find  its  specific  gravity  with  reference  to 
hydrogen,  and  double  its  vapor  density  gives,  by 
Avogadro's  Rule  ( page  204),  its  molecular  weight. 
Vapor  density  determinations  are  then  indispen- 
sable in  the  fixing  of  molecular  weights. 

The  methods  of  determining  the  weights  of 
definite  volumes  of  gases  belong  more  to  physics 
than  to  chemistry.  Certain  methods  of  finding 
vapor  densities,  however,  are  so  frequently  used  in 
chemistry  that  they  deserve  attention  here. 

DUMAS'  METHOD.  The  neck  of  a  round-bottomed 
flask  is  drawn  out  to  a  fine  point.  The  flask  is  then 
weighed  and  warmed  a  little,  with  its  point  dipping 
into  the  liquid  (say  alcohol)  whose  vapor  density  is  to 
be  found.  As  the  air  expanded  by  the  warming  cools 

[214] 


Determining  Molecular  and  Atomic  Weights     215 


and  contracts,  some  alcohol  is  drawn  into  the  flask. 
The  flask  is  now  placed  in  a  vessel  (Fig.  33)  containing 
water  or  oil,  the  temperature  of  which  is  raised  some- 
what above  the  boiling  point  of  alcohol.  The  alcohol 
vaporizes  and  drives  the  air 
from  the  flask  until  finally 
the  vapor  fills  the  flask  at 
the  temperature  of  the  bath 
and  the  barometric  pressure. 
The  tip  of  the  flask  is  then 
sealed  by  melting  it  in  a 
blowpipe  flame,  and  the  flask 
removed  and  weighed.  The 
tip  is  broken  off  under  a 
liquid  such  as  water  or  mer- 
cury, and  the  volume  of  the 
flask  found  by  measuring  the 
amount  of  the  liquid  which 
enters  the  flask. 

An  example  will  make     ( 

the  calculations  clear :          Fig  33_APPARATUS  FOR  DETERMINING 

LieblPf,  in    l8^q,  found      THE    VAPOR    DENSITY    OF    A    LIQUID   BY 

that  a  flask  containing 

289.5  c'c'  °f  dry  air  at  12.8°  and  751  mm-  weighed  48.332  £"-. 
When  filled  with  the  vapor  of  aldehyde  at  53.5°  and 
751  mm-  it  weighed  48.47 1*"-.  What  is  the  vapor  density 
of  aldehyde  ? 

So  hit  ion :  The  real  weight  of  the.  flask  filled  with  aldehyde 
vapor  is  equal  to  its  apparent  weight  (48.471^-)  increased  by  the 
weight  of  the  air  it  would  contain  at  12.8°  and  j$imm..  To  find 
what  this  weight  would  be,  it  is  necessary  to  calculate  the  volume 
at  o°  and  ^famm.  which  289.5  c-c'  of  dry  air  at  I2-8°  an<^  751  mm" 
would  occupy.  This  volume  on  calculation  comes  out  273.1  c.c.. 
Now  as,  under  standard  conditions,  i  c.c.  of  dry  air  weighs  o. 00129^ 
the  273.  i  c.c.  weigh  0.3523^"-.  Adding  this  to  the  apparent  weight 
(48. 47  !<?••)  we  find  the  true  weight  of  the  flask  filled  with  aldehyde 
vapor  to  be  48.8233^-.  Subtracting  the  weight  of  the  flask  from 
this  gives  o.49i3<£"-  as  the  weight  of  the  aldehyde  vapor. 

This  weight  occupies  at  53.5°  and  751  mm-  a  volume  of  289.5^^-, 
which  when  reduced  to  standard  conditions  becomes  239.3^-^; 
239-3  c-c-  of  aldehyde  vapor  weighing  o.49i3<f-,  i  c-c-  would  weigh 


2l6 


Elementary  Chemistry 


0.4913/239.3  =  0.002053;  and  as  i  c-c-  of  hydrogen  under  normal 
conditions  weighs  o.  00009  <£"•,  the  vapor  density  of  aldehyde  is 
0.002053  /o. 00009  =  22-8- 

VICTOR  MEYER'S  METHOD.  The  apparatus  (Fig-.  34) 
consists  of  a  "jacketing  tube,"  B,  the  lower  end  of 
which  is  somewhat  enlarged.  In  this  jacket- 
ing tube  is  suspended  the  tube  CA,  which 
has  a  delivery  tube  at  D,  the  mouth  of  which 
is  placed  under  a  graduated  tube  E  filled 
with  water  and  inverted  in  the  pneumatic 
trough  F.  Suppose  the  vapor  density  of 
chloroform  is  to  be  determined.  A  few 
drops  are  weighed  out  on  a  delicate  balance 
to  tenths  of  milligrams  in  a  tiny  glass-stop- 
pered bottle.  Water  is  boiled  in  B,  the 
rapidity  of  the  boiling  being  so  regulated 
that  the  steam  is  condensed  before  it  reaches 
the  mouth  of  B.  In  this  way  the  tube  CA 
is  heated  throughout  its  wider  portion  to 
nearly  100°.  The  stopper  of  the  bottle  is 
loosened  a  little  and  then  bottle  and  stopper 
are  dropped  into  the  tube  CA,  which  is 
immediately  closed  with  a  rubber  stopper. 
As  chloroform  boils  at  62°,  it  is  rapidly  con- 
verted into  a  vapor  which  forces  out  the 
stopper  of  the  bottle,  and  then  lifts  up  the 
air  in  the  tube,  which  is  thereby  pushed 
over  into  the  graduated  tube.  The  volume 
of  this  air  at  the  temperature  and  pressure 
of  the  room  is  equal  to  the  volume  that  the 
chloroform  vapor  would  occupy  if  it  could 
be  cooled  to  the  same  temperature  without 
condensation.  When  the  weight  and  the 
volume  of  the  chloroform  vapor  have  thus 
been  determined,  its  density  is  calculated  in  a  way 
similar  to  the  following  : 

V.  Meyer  and  C.  Meyer,  in  1878,  determined  the 
vapor  density  of  iodin,  using  in  the  jacketing  tube  a 
liquid  whose  boiling  point  is  26 1  °.  o.  1 1 5  7  ff-  of  iodin  were 
taken  and  the  volume  of  the  air  displaced  was  n.6c-c-  at 
16.1°  and  722.3  m™-.  Find  the  vapor  density  of  iodin. 


C 


Fig.  34 
APPARATUS 
FOR  DETER- 
MINING THE 
VAPOR  DEN- 
SITY OF  A 
LIQUID  BY  VIC- 
TOR MEYER'S 

METHOD 


Determining  Molecular  and  Atomic  Weights     217 

Solution:  As  the  air  was  collected  over  water,  its  vapor 
tension  (i3.6mm.  at  16°,  cf.  §28)  must  be  subtracted  from  the 
barometric  pressure.  The  n.6  c.c.  of  air  reduced  to  standard  and 
dry  conditions  would  then  occupy  10.22  c.c.^  which  would  also  be 
the  volume  of  0.1157^"-  of  iodin,  if  it  could  remain  gaseous  at  o°  and 
760 mm..  One  cubic  centimeter  of  iodin  would  then  weigh 
0.1157/10.22  =  0.01132^-,  and  as  one  cubic  centimeter  of  hydrogen 
under  normal  conditions  weighs  o.oooog^-,  the  vapor  density  of 
iodin  is  0.01132/0.00009  =  125.8. 

252.  Other  Methods  of  Determining  Molecular 
Weights.     Many  substances  are  so  involatile  or  so 
readily  decomposed  at  elevated  temperatures  that 
their  vapor  densities  cannot  be  determined.     Of  the 
other  methods  that  have  been  devised,  those  that 
have  to  do  with  substances  in  a  state  of  solution 
have  received  a  wide  application. 

253.  Analogy   Between   the    Gaseous  and   the 
Dissolved  States.     The  condition  of  a  substance  in 
solution  resembles  in  many  particulars  its  condition 
when  vaporized.     In  both  states  the  molecules  are 
comparatively  far  apart.     Just  as  a  gas  spreads  out 
and  occupies  any  volume  allowed  it,  so  does  a  dis- 
solved substance  sprea4  out  and  occupy  the  volume 
of  the  solvent.     A  liquid  placed  in  a  vacuum  vapor- 
izes  and   the   amount   of   vapor    formed    depends 
mainly  upon  the  temperature.     A  solid  dissolves 
when  placed  in  a  suitable  liquid  and  the  amount 
dissolved  also  depends  to  a  certain  extent  upon  the 
temperature.     These  and  many  other  analogies  led 
van't   Hoff   in    1886  to   apply  the   Gas   Laws   and 
Avogadro's  Hypothesis  to  solutions. 

254.  Osmotic  Pressure.     The  analogy  between 
the  gaseous  and  dissolved  states  is  so  close  that 
we  should  expect  to  find  in  solutions  something 
analogous  to  one  of  the  most  characteristic  features 


218  Elementary  Chemistry 

of  gases,  viz.,  that  of  pressure.  And  indeed  it  may 
be  shown  that  dissolved  substances  exert  a  pressure 
quite  analogous  to  that  of  gases.  All  that  is  needed 
to  bring  into  evidence  this  osmotic  pressure  is  to 
separate  a  solvent  from  its  solution  by  a  sieve-like 
partition  or  semi-permeable  membrane,  which  will  per- 
mit the  molecules  of  the  solvent  to  pass  through, 
but  will  prevent  the  passage  of  the  dissolved  mole- 
cules. The  dissolved  molecules  press  against  this 
membrane,  and  if  any  device  for  measuring  pres- 
sure be  connected  with  the  solution,  its  amount  may 
be  measured.  The  result  of  the  action  of  this  pres- 
sure is  that  the  volume  of  the  solution  increases, 
since  more  and  more  molecules  of  the  solvent  pass 
through  the  partition  to  occupy  the  space  between 
the  mutually  repellent  molecules  of  the  dissolved 
substance.  The  direct  measurement  of  osmotic 
pressures  is  difficult,  as  suitable  semi-permeable 
membranes  are  not  easy  to  prepare.  It  has  been 
proved,  however,  that  the  lowering  of  the  freezing 
point  or  the  raising  of  the  boiling  point  of  a  liquid 
brought  about  by  the  solution  of  another  substance 
is  directly  proportional  to  the  osmotic  pressure. 
Hence,  freezing  and  boiling  point  determinations 
enable  us  to  ascertain  indirectly  osmotic  pressures. 
255.  Depression  of  the  Freezing  Point  of  Solu- 
tions. A  method  of  ascertaining  the  molecular 
weights  of  dissolved  substances  had  been  worked 
out  by  Raoult  in  1882,  some  time  before  van't  Hoff 
had  put  forth  his  Theory  of  Solutions.  It  depends 
upon  the  lowering  of  the  freezing  point  of  a  solution 
due  to  the  addition  of  some  soluble  substance. 
Raoult  found  that : 


Determining  Molecular  and  Atomic  Weights     219 

When  in  equal  amounts  of  the  same  solvent,  equal 
weights  of  different  substances  are  dissolved,  the  depres- 
sions of  the  freezing  point  vary  inversely  as  the  molecular 
weights  of  the  dissolved  substances. 

If  m  and  m'  are  the  molecular  weights  of  two  sub- 
stances, and  /  and  I'  are  the  corresponding  depres- 
sions of  the  freezing  point  produced  by  the  solu- 
tions of  equal  weights  of  the  substances  in  the  same 
amounts  of  the  solvent,  then : 

m  :  m'  :  :  I'  :  I 

Whence,  m'  I' 

m-    — 

To  start  with,  it  is  necessary  that  the  molecular 
weight  of  one  substance  in  solution  be  known. 
This  has  to  be  found  by  a  vapor  density  determina- 
tion. The  depression  of  the  freezing  point  brought 
about  by  dissolving  one  gram  of  this  substance  in 
100^-  of  the  solvent  is  determined  once  for  all, 
and  this  represents  the  product  m'  I' ,  which  thus 
has  a  constant  value.  One  gram  of  a  substance  of 
unknown  molecular  weight  is  then  dissolved  in 
100^.  of  the  same  solvent,  and  the  lowering  of  the 
freezing  point  determined.  From  these  data  the 
unknown  molecular  weight  may  be  calculated  by 
means  of  the  above  formula. 

256.  Elevation  of  Boiling  Points.  A  law  very 
similar  to  that  for  the  depression  of  the  freezing 
point  was  also  established  by  Raoult  with  reference 
to  the  raising  of  the  boiling  point  of  a  liquid  by 
solution  of  a  substance.  If  b  and  £',  representing 
the  boiling  points  of  solutions  of  the  same  strength 
of  different  substances  in  the  same  solvent,  be 


22O  Elementary  Chemistry 

substituted  for  /  and  I'  in  the  previous  paragraph, 
the  expression : 

m'  b' 

m  = 

b 

is  the  algebraic  statement  of  the  law  in  question. 
The  elevation  of  the  boiling  point  occasioned  by  dis- 
solving one  gram  of  a  substance  of  known  molecular 
weight  in  locX-  of  the  solvent  is  found,  from  which 
the  value  of  the  constant  m'  b'  is  calculated.  One 
gram  of  a  substance  of  unknown  molecular  weight 
is  dissolved  in  loo^-  of  the  solvent,  and  from  the  rise 
in  boiling  point  the  molecular  weight  is  computed. 

257.  Specific  Heat.     Different  amounts  of  heat 
are  required  to  warm  equal  weights  of  different  sub- 
stances through  the  same  temperature  interval,  and 
the  ratio  of  the  amount  of  heat  required  to  warm 
a  given  (unit)  weight  of  a  substance  through  one 
degree  to  the  amount  of  heat  required  to  warm  an 
equal  weight  of  water  through  one  degree  is  called 
the  specific  Jicat  of   that   substance.      Inasmuch  as 
water  has  the  greatest  capacity  for  absorbing  heat, 
of  all  known  definite  chemical  substances,  specific 
heats  are  less  than  unity  and  are  usually  expressed 
as  decimal  fractions. 

258.  Dulong   and    Petit 's    Law.     In    1819  two 
French  chemists,  Dulong  and  Petit,  determined  the 
specific  heats  of  a  number  of  elements,  and  found 
that  the  products  of  the  atomic  weights  and  the 
specific  heats  of  the  elements  were  approximately 
the  same.     This  product  is  termed  the  atomic  heat, 
and  the  Law  may  be  stated  as  follows : 

The  atomic  heats  of  all  the  elements  are  the  same. 


Determining  Molecular  and  Atomic  Weights     221 
A  few  data  will  serve  to  illustrate  this  law : 


ELEMENT 

Specific 
Heat 

Atomic 
Weight 

Atomic 
Heat 

Mercury          

0.032 

200 

6  4 

Zinc 

0.008 

6<;  4 

6  5 

Silver 

O  OSQ 

IO7  O 

6  4. 

Gold 

o  033 

197.2 

6  5 

The  Law  may  also  be  put  in  this  way : 
The  specific  heats  of  elements  are  inversely  proportional 
to  their  atomic  weights. 

259.  Determination  of  Atomic  Weights  with  the 
Aid  of  Dulong  and  Petit's  Law.  To  apply  Dulong 
and  Petit's  Law  we  have  merely  to  divide  the  con- 
stant number,  6.4,  by  the  specific  heat  of  the  ele- 
ment in  question,  and  the  quotient  is  approxi- 
mately the  atomic  weight  sought.  Thus,  suppose 
we  have  found  the  specific  heat  of  lead  to  be  0.031. 
Dividing  6.4  by  0.031  we  get  206.5  as  the  required 
atomic  weight.  While  results  by  this  method  are 
not  very  exact,  they  yet  serve  to  distinguish 
between  two  questionable  atomic  weights  for  the 
same  element.  Thus,  lead  forms  several  oxids,  the 
analysis  of  which  shows  that  the  atomic  weight  of 
lead  may  be  either  206  or  103.  Of  these  the  specific 
heat  shows  that  206  is  to  be  chosen. 

METHODS  BUT  APPROXIMATE.  The  foregoing  methods 
are  all  at  best  mere  approximations  ;  they  simply  fur- 
nish a  means  of  deciding  between  a  molecular  weight 
and  some  multiple  of  it.  The  accurate  values  are  found 
only  by  means  of  quantitative  analyses.  Thus,  the  for- 
mula of  silver  chlorid  is  AgCl  or  some  multiple  of  AgCl, 
as  Ag2Cl2  or  Ag3Cl3.  The  molecular  weight  of  AgCl 
is  143.28.  The  vapor  density  of  silver  chlorid  has  been 
found  to  be  82,  from  which,  by  Avogadro's  Hypothesis, 


222  Elementary  Chemistry 

a  molecular  weight  of  164  is  obtained.  Now  although 
143.28  and  164  are  by  no  means  equal,  yet  they  are  more 
nearly  equal  than  are  164  and  2  x  143.28  (—  287.56),  so 
that  there  is  no  doubt  but  that  the  formula  AgCl  is 
best  in  accordance  with  the  hypothesis. 

Problems 

1.  Dumas  and  Peligot,  in  1835,  found  that  a  flask  of  484  c.c. 
capacity  weighed  at  21°  and  ifomm.  lost  0.069^.  when  filled  with 
the  vapor  of  wood  alcohol  at  100°.      Find  the  vapor  density  of 
wood  alcohol. 

2.  V.  Meyer  and  H.  Biltz,  in  1889,  found  that  when  o. 0589 g-  of 
silver  chlorid  was  vaporized  at  1736°  it  displaced  8.6  c.c.  Of  nitrogen 
(with  which  the  apparatus  was  filled),  at  a  temperature  of  13.40, 
and  a  pressure  of  752.7,  the  nitrogen  being  collected  over  water. 
What  is  the  vapor  density  of  silver  chlorii? 

j.  0.1561^"-  of  a  compound  in  a  Victor  Meyer's  vapor-density 
apparatus  expelled  32.1  c.c.  of  dry  air  at  20°  and  744 mm..  What  is 
(a)  its  vapor  density,  (b]  its  molecular  weight? 

4.  What  is  the  formula  of  mercuric  chlorid  as  deduced  from 
the  following  data?    Weight  of  flask  full  of  vapor  at  350°  and 
758.4*»w.  =  27.40I.?'-.     Capacity  of  globe  =  250^-. 

5.  Determine  the  vapor  density  of  phosphorus  trichlorid  from 
the  following  data :    Weight  of  flask  full  of  vapor  at  100°  and 
761  mm.  —  40. 773 g-.     Capacity  of  globe  =  280  c.c., 

6.  What  is  the  vapor  density  of  ether  as  calculated  from  the 
following  data:   Weight  of  flask  full  of  air  at  19°  and  741. $mm- 
=  49.632<?"-.     Weight  of  flask  full  of  vapor  at  82.5°  and  740.3 mm. 
= 49.995^..     Weight  of  flask  full  of  water  at  4°  =  325.61  g-. 

7.  Applying  Dulong  and  Petit's  Law,  calculate  the  specific 
heats  of  the  following  elements  (their  atomic  weights  are  placed 
in   parentheses):    Aluminum  (27),   manganese '(55),   sodium  (23), 
iron  (56). 

8.  The  specific  heat  of  phosphorus  is  0.189,  and  its  vapor 
density  referred  to  hydrogen  is  62.     How  many  atoms  are  there 
in  a  molecule  of  phosphorus  gas? 


CHAPTER    XXI 


SULFUR  AND  ITS  COMPOUNDS 

260.  Occurrence.    Sulfur  occurs  free  principally 
in  Sicily,  Mexico,  and  Louisiana.     Its  compounds 
are  numerous  and  widespread ;  the  principal  ones 
are   iron   bisulfid,   FeS2   (pyrites),  lead   sulfid,   PbS 
(galenite),  zinc  sulfid,  ZnS   (zinc   blende),  antimony 
sulfid,  Sb2S3   (stibnite),  and  hydrated  calcium  sul- 
fate,  CaSO4  +2  H2O  (gypsum).     It  is  also  a  constit- 
uent of  some  animal  and  vegetable  products,  as 
eggs,  mustard,  horseradish,  onions,  and  garlic. 

261.  Preparation.    Native  sulfur  is  usually  con- 
taminated with  earthy  material.     To  free  it  from 
this,  it  is  heaped  up  on  sloping  ground,  in  such  a 
way  that  air  can  be  admitted  to  the  interior,  covered 
over  loosely  with  earth  and  set  fire  to.     Somewhat 
less  than  half  of  the  sulfur  burns  to  furnish  heat 
enough  to  melt  the  other  half,  which  flows  down 
and  collects  in  wooden  troughs,  leaving  the  earthy 
impurities  behind. 

The  sulfur  thus  obtained  is  purified  by  distilla- 
tion ;  the  vapor  passes  into  a  large  condensing 
chamber,  where  some  of  the  sulfur  collects  as  a 
light  powder,  known  as  flowers  of  sulfur,  while  the 
rest  collects  in  liquid  form  at  the  bottom  and  is 
drawn  off  into  molds,  giving  the  form  of  sulfur 
called  roll  sulfur  or  brimstone.  Lac  sulfur  is  or  milk 
of  sulfur  is  obtained  by  the  action  of  hydrochloric 
acid  on  alkalin  solutions  of  polysulfids. 

[  223] 


224  Elementary  Chemistry 

262.  Properties.     Physical.     (Table    I.,  Appen- 
dix D.)     Sulfur  is  a  yellow  solid,  appearing  nearly 
white  when  finely  divided,  without  odor  or  taste. 
It  is  insoluble  in  water,  but  readily  soluble  in  car- 
bon bisulfid,  excepting  a  few  of  its  allotropic  modi- 
fications.    It  is  a  non-conductor  of  electricity  and  a 
poor  conductor  of  heat. 

Chemical.  Sulfur  ignites  at  about  260°  in  the  air, 
burning  to  sulfur  dioxid,  SO2.  It  enters  into  com- 
bination with  most  elements  at  high  temperatures, 
forming  sulfids. 

263.  Allotropic  Forms.     Sulfur  generally  occurs 
in  nature,  and  also  crystallizes  from  its  carbon  bisul- 
fid solution,  in  rhombs.     Melted  sulfur  crystallizes 
in  transparent,  needle-shaped  crystals  which  at  ordi- 
nary temperatures  change  into  the  rhombic  variety. 
Sulfur  melts  at  1 14°  to  a  mobile,  amber-colored  liquid 
which  at  1 70°  assumes  a  darker  color  and  becomes 
so  thick  and  viscid  as  not  to  run  out  when  the  vessel 
containing  it  is  inverted.     At  about  270°  it  turns 
darker  still,  but  regains  in  part  its  mobility.     If, 
just  before  it  boils,  it  is  suddenly  cooled  by  pouring 
it  into  water,  it  forms  a  rubber-like  mass.     This 
plastic  sulfur  gradually  turns  into  the  rhombic  form. 

264.  Uses.   Sulfur  is  used  in  making  sulfuric  acid, 
matches,  gunpowder,  fireworks,  in  vulcanizing  rub- 
ber, and  in  medicine. 

HYDROGEN  SULFID,  H}S     (Sulfuretted  Hydrogen) 

265.  Occurrence.     Certain  volcanic  gases  and 
the  water  from  "sulfur  springs"  contain  free  hydro- 
gen sulfid.     It  is  also  liberated  by  the  decomposi- 
tion of  some  animal  substances,  as  eggs. 


MENDELEBFF 


MOISSAN 


RAMSAY  DEWAR 

Plate   VI 


HENRI  MOISSAN  DIMITRI  IVANOVITCH  MENDELEEFF 

1852 ;  French  1834  ;  Russian 

Isolated  fluorin.     Perfected  the  Discovered    the    Periodic    Law. 

electric  furnace,  and  by  its  aid  Studied  specific  gravities  of  solu- 

prepared    artificial    diamonds,  fions  and  investigated  geological 

rare  metals,  and  compounds  .  chemistry 


JAMES  DEWAR  WILLIAM  RAMSAY 

1842" ;  English  ,     1852 ;  English 

Solidified  hydrogen  and  is  very  Active  in  physical  and  inorganic 

active  in  applications  of  low  tcm-  chemistry.      Discovered    argon, 

peratures  to  chemical  problems  helium,  neon,  krypton,  and  xenon 


Plate  VI 


Sulfur  and  its  Compounds  225 

266.  Preparation.     Hydrogen  sulfid  is  prepared 
by  the  action  of  dilute  sulfuric  or  hydrochloric  acid 
on   metallic   sulfids ;    iron    sulfid,    FeS,    is   usually 
employed : 

FeS  +  2  HC1  or  H2SO4  ->  FeCl2  or  FeSO4  +  H2S 

267.  Properties.     Physical.     Hydrogen  sulfid  is 
a  colorless  gas  of  rather  a  sweet  taste  and  a  smell 
resembling  that  of  rotten  eggs.     It  is   soluble   in 
about  a  third  its  volume  of  water. 

Chemical.  Hydrogen  sulfid  burns  with  a  blue 
flame : 

2H2S  +  3  O2-*  2H2O  +  2SO2 

It  is  decomposed  by  the  halogens  with  the  separa- 
tion of  sulfur  and  the  formation  of  the  correspond- 
ing hydracid : 

H2S  +  C12  -^2HC1  +  S 

It  acts  upon  many  metallic  salts  with  the  formation 
of  sulfids.  Its  aqueous  solution  decomposes  readily 
when  exposed  to  the  air;  the  oxygen  of  the  air 
combines  with  the  hydrogen  in  the  sulfid  to  form 
water,  and  the  sulfur  is  set  free.  Air  containing 
but  a  vsmall  proportion  of  it  gives  headache  and 
nausea  to  the  one  breathing  the  mixture,  while  in 
larger  proportions  it  produces  unconsciousness  and 
finally  death. 

COMPOSITION.  Tin,  heated  in  hydrogen  sulfid  gas, 
combines  with  the  sulfur  and  leaves  a  volume  of  hydro- 
gen equal  to  that  of  the  gas  taken.  Hence,  hydrogen 
sulfid  contains  an  equal  volume  of  hydrogen.  Two 
volumes  of  hydrogen  sulfid  react  with  three  volumes  of 
oxygen  to  give  two  volumes  of  water  vapor  and  two 
volumes  of  sulfur  dioxid.  This  shows  that  two  volumes 
of  hydrogen  sulfid  contain  two  volumes  of  hydrogen, 


226  Elementary  CJiemistry 

for   two  volumes   of  hydrogen   are  contained   in  two 
volumes  of  water  vapor. 

HYDROGEN  DISULFID,  H2S2.  Hydrogen  disulfid  is 
prepared  by  decomposing  a  polysulfid  of  calcium  with 
dilute  hydrochloric  acid.  It  is  a  liquid  with  an  odor 
similar  to  that  of  hydrogen  sulfid,  but  much  more  pen- 
etrating. It  is  quite  unstable,  decomposing  slowly  into 
hydrogen  sulfid  and  sulfur. 

268.  Sulfids.    Sulfur  combines  with  many  other 
elements  to  produce  sulfids.     The  union  is  often 
accompanied  with  the  evolution  of  much  heat  and 
light,  as,  for  example,  in  the  case  of  iron  and  sulfur. 
Sulfids  may  also  be  prepared  by  passing  hydrogen 
sulfid  into  solutions  of  metallic  compounds,  where- 
by, as  all  sulfids  except  those  of  the  alkali  and  alka- 
lin  earth  metals  are  insoluble  in  water,  the  metallic 
sulfids  are  precipitated.     Hydrogen  sulfid  gas  acts 
upon  many  metals,  covering  them  with  a  coating 
of  the  respective  sulfid.     The  tarnishing  of  silver  is 
due  to  the  action  of  the  extremely  minute  amounts 
of  this  gas  present  in  the  air.     Silver  spoons  are 
tarnished  by  the  action  of  the  sulfur  compounds 
in  mustard  and  eggs.     Lead  sulfid  is  black ;  hence 
houses   painted  with  white  lead  paint  often  turn 
dark  from  the  hydrogen  sulfid  in  the  air. 

269.  Carbon  Bisulfid,  CS2.     When  sulfur  vapor 
comes  in  contact  with  red-hot  carbon    (charcoal), 
union  ensues,  and  a  compound  of  the  two  elements, 
carbon  bisulfid,  CS2,  is  produced.     Carbon  bisulfid 
is  a  colorless,  mobile  liquid,  with  a  pleasant  odor 
when  pure,  but  when  exposed  to  light  it  slowly 
decomposes  into  black,  ill-smelling  solids.     It  re- 
fracts light  strongly  and  is  used  as  a  solvent  for 
rubber  and  sulfur.     Its  ignition  temperature  is  low 


Sulfur  and  its  Compounds  227 

and  the  products  of  its  combustion  are  sulfur  dioxid 
and  carbon  dioxid : 

CS2  +  3  O2  — >  CO2  +  2  SO2 

SULFUR   DIOXID 

270.  Occurrence.     Sulfur   dioxid    is   found  in 
most  volcanic  gases. 

271.  Preparation.     The  simplest  method  of  pre- 
paring sulfur  dioxid  consists  in  burning  sulfur  or 
compounds  rich  in  sulfur,  as  iron  pyrites,  FeS2 : 

S  +  02  ->  S02 
4FeS2  +  iiO2  — >  2Fe263  +  8SO2 

Copper  and  some  other  metals  when  heated  with 
strong  sulfuric  acid  decompose  it  with  liberation  of 
sulfur  dioxid.  So  also  does  carbon,  thus : 

C  +  2H2S04  ->C02  +  2S02  +  2H20 

A  convenient  method  consists  in  the  action  of  dilute 
hydrochloric  acid  on  sodium  sulfite,  Na2SO3  : 

Na2SO3  +  2  HC1  -»  2  NaCl  +  H2O  +  SO2 

272.  Properties.     Physical.     Sulfur   dioxid   is  a 
colorless  gas  of  suffocating  odor,  and  heavy  enough 
to  be  collected  by  downward  displacement  like  car- 
bon dioxid.     Water  dissolves  about  fifty  times  its 
own    volume    of    it.     The  gas  may  be  converted 
into  a  colorless  liquid  at  the  temperature  of  a  freez- 
ing mixture  of  ice  and  salt  and  this  liquid  at  — 76° 
turns  into  a  transparent  solid. 

Chemical.  Sulfur  dioxid  is  a  non- supporter  of 
combustion  in  general,  but  ignited  potassium  or 
magnesium  continue  to  burn  in  it,  and  finely  divided 
metals,  as  iron,  will  even  take  fire  when  introduced 


228  Elementary  Chemistry 

into  it.  Its  aqueous  solution  has  acid  properties, 
and  it  is  probable  that  sulfurous  acid,  H2SO3,  is 
formed. 

COMPOSITION.  When  sulfur  is  burned,  the  volume 
of  the  resulting  sulfur  dioxid  is  equal  to  that  of  the 
oxygen  used.  Hence,  equal  volumes  of  sulfur  vapor 
and  oxygen  are  contained  in  it. 

273.  Uses.     Sulfur  dioxid  is  used  in  enormous 
quantities  in  the  manufacture  of  sulfuric  acid.     Its 
use  as  a  disinfectant  is  well  known  (sulfur  candles). 
It  is  also  used  in  bleaching  and  in  paper-making. 

BLEACHING.  Sulfur  dioxid  bleaches,  not  by  destroy- 
ing the  coloring  matter,  but  by  forming  with  it  a  col- 
orless compound.  This  compound  is  decomposed  by 
sulfuric  acid  or  an  alkali,  and  the  original  color  restored. 
A  red  rose  turns  white  when  held  in  the  gas,  but  its 
color  is  restored  by  dipping  it  in  very  dilute  sulfuric 
acid.  The  bleaching  effect  also  disappears  after  a  time, 
so  that  cloth  and  straw  bleached  by  sulfur  dioxid  "yel- 
low "  with  age. 

274.  Sulfur  Trioxid.     Sulfur  trioxid  is  obtained 
by  heating  fuming  sulfuric  acid,  or  by  passing  a  mix- 
ture of  sulfur  dioxid  and  oxygen  over  heated  plat- 
inized asbestos.     It  forms  a  white,  crystalline  solid 
which  melts  at  16°.     When  placed  in  water  it  dis- 
solves with  a  hissing  noise  and  forms  sulfuric  acid. 

COMPOUNDS  OF  SULFUR,  OXYGEN,  AND  HYDROGEN 

275.  Sulfur,  in  combination  with  varying  propor- 
tions of  oxygen  and  hydrogen,  forms  several  acids, 
of  which  only  sulfuric  acid,  H2SO4,  is  important. 

SULFUROUS  ACID,  H2SOV  Sulfurous  acid  is  formed 
when  sulfur  dioxid  is  dissolved  in  water.  It  is  quite 
unstable,  and  is  converted  into  sulfuric  acid  by  standing 


Sulfur  and  its  Compounds  229 

exposed  to  the  air  for   some  time.      It  forms  several 
important  and  stable  salts,  however. 

SULFURIC  ACID 

HISTORICAL  NOTE.  Sulfuric  acid  has  been  known 
since  the  eighth  century,  when  it  was  prepared  by  dis- 
tilling green  vitriol  (ferrous  sulfate).  Towards  the  end 
of  the  eighteenth  century  the  "lead-chamber  method" 
of  manufacture  was  devised,  and  within  the  last  few 
years  the  "contact  process"  has  been  perfected. 

276.  Occurrence.     Free  sulfuric  acid  is  found  in 
small  quantities  in  the  water  of  some  rivers  whose 
sources  are  in  volcanic  districts.     Its  compounds 
with  metals,  the  sulfates,  are  quite  common ;  gyp- 
sum,  a    sulfate   of    calcium,   CaSO4,   is   especially 
abundant. 

277.  Preparation.     Sulfuric  acid  is  never  pre- 
pared in  the  laboratory  except  as  an  illustration  of 
the  industrial  process.     The  principle  of  this  process 
consists  in  the  oxidation  of  sulfur  dioxid  to  trioxid 
and  the  union  of  the  latter  with  water.      The  con- 
version of  the  dioxid  into  the  trioxid  is  effected  by 
means  of  platinized  asbestos  or  the  higher  oxids  of 
nitrogen.    These  give  up  a  portion  of  their  oxygen 
to  sulfur  dioxid,  and  immediately  take  it  up  again 
from  the  air,  which  must  always  be  present.     The 
nitrogen  compounds  thus  act  as  carriers  of  oxygen 
from  the  air  to  the  sulfur  dioxid.     Theoretically,  a 
very  small  amount  of  them  should  suffice  to  oxidize 
a  very  large  amount  of  the  sulfur  dioxid,  but  prac- 
tically there  is  a  limit  to  the  amount. 

THEORY  OF  THE  PROCESS.  Several  theoretical  expla- 
nations of  the  process  of  oxidation  have  been  advanced, 
of  which  that  due  to  Lunge  is  perhaps  the  most  satis- 
factory. He  assumes  that  the  sulfur  dioxid  combines 


Sulfur  and  its  Compounds  231 

with  the  oxids  of  nitrogen  and  water  to  form  nitrosyl- 
sulfuric  acid,  SO2(NO2)OH,  so  called  from  nitrosyl,  the 
name  of  the  radical  NO2. 

S02  +  HN03  -»  S02(N02)OH 
This  reacts  with  steam  thus  : 

2SO2(NO2)OH  +  H2O  — >  2H2SO4  +  NO  +  NO2 

The  nitrogen  oxids  react  with  more  sulfur  dioxid, 
oxygen  (from  the  air),  and  steam  : 

2  S02  +  NO  +  N02  +  02  +  H20  ->  2  S02(N02)Of 

The  nitrosyl-sulfuric  acid  thus  formed  is  decomposed 
by  steam  as  above,  and  these  reactions  repeat  them- 
selves. The  process  becomes  continuous  and  the  oxids 
of  nitrogen  are  used  again  and  again. 

278.  Practice  of  the  Process.  (Fig.  35.)  The 
sulfur  dioxid  is  obtained  by  burning  sulfur  or  iron 
pyrites,  FeS2,  in  a  suitable  furnace.  The  dioxid 
mixed  with  air  passes  from  the  furnace  at  a  tem- 
perature of  about  300°  into  the  bottom  of  a  tall 
tower,  called  "Glover's  tower,''  which  is  lined  with 
leau  and  filled  with  large  fragments  of  brick  below 
and  smaller  pieces  of  coke  above.  Down  this  tower 
trickles  dilute  sulfuric  acid  mixed  with  nitric  acid 
and  nitrogen  oxids  ("niter-acid").  As  the  hot 
gases  rise  they  carry  off  with  them  as  vapor  most 
of  the  water  and  nitrogen  compounds  dissolved  in 
the  sulfuric  acid,  so  that  a  "strong  acid  "  free  from 
nitrogen  compounds  flows  out  at  the  base  of  the 
tower. 

By  passing  through  the  "Glover"  the  mixture 
of  gases  is  cooled  down  to  about  70°,  the  temper- 
ature which  is  most  favorable  for  the  oxidation  of 
the  sulfur  dioxid. 


232  Elementary  Chemistry 

On  leaving  the  "  Glover  "  the  gaseous  mixture 
passes  into  the  first  of  three  or  four  immense  cham- 
bers lined  with  lead,  into  which  steam  is  blown. 
The  oxidation  takes  place  as  the  gases  pass  through 
the  chambers  and  the  sulfuric  acid  formed  collects 
at  the  bottom  of  the  chambers,  where  it  is  drawn 
off  from  time  to  time.  The  oxidation  is  almost 
complete  when  the  gases  leave  the  second  chamber. 
No  steam  is  blown  into  the  last  chamber,  so  that 
the  residual  gases  may  cool  off  a  little. 

The  gases  escaping  from  the  last  chamber 
contain  nitrogen  compounds  which  are  caught  in 
another  tower,  called  "  Gay-Lussac's  tower."  Down 
the  coke  with  which  it  is  filled  trickles  concentrated 
sulfuric  acid,  which  dissolves  out  the  nitrogen  com- 
pounds in  the  ascending  gases.  Only  the  waste 
gases,  such  as  the  nitrogen  from  the  air  used  in 
the  burning  of  the  pyrites,  escape  from  the  "Gay- 
Lussac"  into  the  chimney  which  causes  the  draft 
through  the  chambers.  The  acid  collecting  at  the 
base  of  the  "Gay-Lussac"  is  forced  up  into  a  tank 
above  the  "  Glover,"  by  means  of  compressed  air, 
and  its  nitrogen  compounds  as  well  as  most  of  its 
water  removed  by  flowing  down  the  "Glover"  as 
stated  above.  The  process  is  thus  seen  to  be  con- 
tinuous. The  acid  obtained  from  the  lead  cham- 
bers is  called  "  chamber  acid,"  and  contains  about 
35  per  cent  of  water.  This  is  strong  eno  ^h  for 
many  uses,  but  most  of  it  is  concentrated  in  ;ead  or 
cast-iron  pans  until  it  contains  about  23  per  ^ent  of 
water,  when,  as  the  acid  now  begins  to  act  upon 
the  metal,  its  further  concentration  is  effected  by 
heating  it  in  platinum  vessels. 


Sulfur  and  its  Compounds  233 

MANUFACTURE  BY  THE  CONTACT  METHOD.  Although 
it  has  been  known  for  many  years  that  sulfur  trioxid  is 
formed  when  a  mixture  of  sulfur  dioxid  and  oxygen  (air) 
is  passed  over  heated  platinized  asbestos,  the  commercial 
application  of  the  process  was  hindered  by  the  fact  that 
the  catalytic  agent  soon  lost  its  efficacy.  Recently,  how- 
ever, it  has  been  found  that  by  thoroughly  washing  the 
gaseous  mixture,  the  life  of  the  platinized  asbestos  and 
also  of  other  "catalyzers"  can  be  prolonged  so  as  to 
make  the  process  of  commercial  value.  Another  diffi- 
culty in  the  process  that  had  also  to  be  overcome  was 
the  delicate  regulation  of  the  temperature  required. 
The  contact  process  is  being  introduced  rapidly  into 
chemical  works  and  bids  fair  to  become  a  serious  com- 
petitor of  the  lead-chamber  process. 

279.  Properties.  Physical.  Sulfuric  acid  is  a 
thick,  colorless  liquid  of  oily  appearance.  It  mixes 
in  all  proportions  with  water,  and  the  mixing  is 
accompanied  with  the  evolution  of  much  heat.  To 
avoid  spattering  the  acid  should  be  poured  slowly 
into  the  ivater,  never  the  water  into  the  acid.  When 
exposed  to  the  air  it  absorbs  the  water  vapor  which 
may  be  present  with  great  avidity,  and  thus  makes 
an  excellent  drying  agent. 

Chemical.  Most  animal  and  vegetable  substances 
are  charred  by  strong  sulfuric  acid,  which  removes 
in  part  the  elements  of  water.  At  a  red  heat  the 
acid  decomposes  into  sulfur  dioxid,  oxygen,  and 
water  vapor ;  at  temperatures  near  its  boiling  point 
it  dissociates  into  water  and  sulfur  trioxid  to  a 
limited ;  extent.  It  neutralizes  bases  and  chemically 
dissolves  most  metals,  the  sulfates  of  which  are 
thus  formed,  and  hydrogen  or  sulfur  dioxid  are 
evolved  according  to  the  conditions  of  temperature, 
concentration  of  the  acid,  and  nature  of  the  metal. 


234  Elementary  Chemistry 

280.  Uses.     Sulfuric   acid   is  undoubtedly  the 
most  useful  " chemical";  it  is  employed  in  almost 
all  chemical  industries.     It  is  necessary  in  the  man- 
ufacture of  hydrochloric  (§  202)  and  nitric  (§  174) 
acids,  of   sodium  carbonate  (§225),  of   fertilizers, 
of  glucose,  and  many  other  products. 

281.  Fuming  or  Pyrosulfuric  Acid.     When  iron 
pyrites,  FeS2,  is  exposed  to  the  weather  it  gradu- 
ally takes  up  oxygen  and  becomes  partially  con- 
verted into  iron  sulf ate,  Fe  2  (SO 4 )  3 .    This  is  leached 
out,  evaporated  to  dryness,  and  heated  to  a  high 
temperature  in  earthenware  retorts.     Sulfur  trioxid 
and  iron  oxid  are  the  products,  of  which  the  latter 
remains  in  the  retort  and  the  former  distills  over 
into  receivers  containing  water : 

Fe2(S04)3->Fe203+3S03 
H2O  +  2SO3-^H2S2O7 

This  acid,  sometimes  called  "Nordhausen  oil  of 
vitriol,"  is  probably  a  solution  of  sulfur  trioxid  in 
sulfuric  acid,  for  it  readily  yields  these  compounds 
when  heated.  It  is  an  even  more  energetic  acid 
than  sulfuric.  It  gives  off  fumes  of  sulfur  trioxid 
when  exposed  to  the  air.  Pyrosulfuric  acid  is  now 
almost  exclusively  manufactured  by  the  "  contact 
process." 

THIOSULFURIC  ACID.  Oxygen  and  sulfur  resemble 
each  other  in  many  particulars,  and  sulfur  may  replace 
oxygen  in  several  compounds.  Thiosulfuric  acid, 
H2S2O3,  may  then  be  regarded  as  sulfuric  acid,  H2SO4, 
in  which  one-fourth  of  the  oxygen  has  been  replaced  by 
sulfur.  This  acid  has  not  yet  been  obtained  in  a  pure 
state,  but  some  of  its  salts  are  known ;  sodium  thiosul- 
fate,  Na2S2O3,  commonly  but  erroneously  known  as 


Sulfur  and  its  Compounds  235 

"hyposulfite  of  soda,"  is  the  most  important  because 
of  its  use  in  dyeing  and  photography. 

Exercises 

/.     What  are  the  general  methods  of  preparing  stilfids  ? 

2.  What  acids  form  white  fumes  when  ammonia  is  brought 
near  them  ?  Why  ? 

j.  Given  strong  ammonia  water,  how  can  you  ascertain 
whether  or  not  sulfuric  acid  is  volatile  ? 

4.  What  would  you   think  would  be  produced  by   heating 
solid  ammonium  sulfid,  (NH4).,S  ? 

5.  Devise  simple  and  rapid  tests  for  distinguishing  sodium 
carbonate,    sodium   sulfate,  sodium  sulfid,  and  sodium  formate 
from  one  another. 

6.  What  is  the  objection  to  concentrated  sulfuric  acid  as  a 
drying  agent  for  ammonia  ?    What  compound  can  be  used  to  dry 
ammonia  ? 

7.  In  the  electrolysis  of  dilute  sulfuric  acid  why  is  oxygen 
given  off  at  the  anode  ? 

Problems 

7.  100^-  .of  hydrogen  sulfid  are  burned.  What  gases  result, 
and  how  many  cubic  centimeters  of  each  ? 

2.  How  many  cubic  centimeters  of  sulfur  can  be  obtained 
from  I.OQC.C.  of  sulfur  vapor,  the  temperature  of  which  is  500°  ? 

j.  How  many  grams  of  ferrous  sulfid  are  required  to  prepare 
10 1-  of  hydrogen  sulfid  ? 

4.  How  much  oxygen,  both  by  weight  and  volume,  is  required 
to  burn  100^"-  of  sulfur  containing  12$  of  incombustible  impurities  ? 

5.  If  the  specific  gravity  of  sulfuric  acid  is  i.S,  how  many 
cubic  centimeters  of  the  acid  will  a  liter  flask  contain  ? 

6.  What    weight    and   what    volume    of    hydrogen    can    be 
obtained  from  5.1^"-  of  hydrogen  sulfid  ? 

7.  Berzelius,  in  1818,  converted  lo.ooo^-  of  lead  into  14.642^- 
of  lead  sulfate,  PbSO4.     The  atomic  weights  of  lead  and  of  oxy- 
gen are  206.91  and  16.00.     Calculate  the  atomic  weight  of  sulfur. 

8.  Dumas,  in    1859,  synthesized   silver   sulfid,  Ag2S,  finding 
the  ratio  of  the  weights  of  silver  and  of  the  sulfid  to  be  112.1943  : 
128.8288.     The  atomic  weight  of  silver  is  107.94;  find  the  atomic 
weight  of  sulfur. 


CHAPTER  XXII 

PHOSPHORUS,  ARSENIC,  ANTIMONY,  AND 
BISMUTH 

The  elements  phosphorus,  arsenic,  antimony, 
and  bismuth  not  only  exhibit  certain  similarities 
among  themselves,  but  also  with  nitrogen.  They 
may,  therefore,  be  studied  with  advantage  together. 
In  this  natural  family  there  is  a  gradual  transition 
from  the  non-metals  to  the  metals.  Both  in  phys- 
ical and  in  chemical  properties,  nitrogen  and  phos- 
phorus are  typical  non-metals.  Arsenic  begins  to 
present  metallic  properties,  while  antimony  is 
decidedly  metallic  in  character,  and  bismuth  has  no 
non-metallic  properties  at  all. 

PHOSPHORUS 

HISTORICAL  NOTE.  Phosphorus  was  first  prepared 
by  Brande  in  1669.  He  kept  his  method  secret  at  first, 
but  Kunckel  found  out  what  substance  was  used  in  its 
preparation  and  shortly  afterward  succeeded  in  making 
it  also.  Scheele  a  century  later  invented  the  process 
used  in  manufacturing  phosphorus  from  the  ashes  of 
bones. 

282.  Occurrence.  Phosphorus  is  never  found 
free  in  nature,  but  certain  of  its  compounds  are 
quite  abundant  and  widely  diffused.  Calcium  phos- 
phate, Ca3(PO4)2,  is  found  in  many  places  as  large 
deposits  of  the  minerals  pJwspliorite  and  apatite,  also 
in  guano  deposits  and  in  the  ashes  of  boneSo 

[236] 


Phosphorus,  Arsenic,  Antimony,  Bismuth        237 

283.  Preparation.      Finely  ground  bone  ash  or 
natural  phosphates  are  treated  with  dilute  sulfuric 
acid,  whereby  the  insoluble  phosphate  is  converted 
into  a  soluble  phosphate,  commonly  called  superphos- 
phate of  lime,  and  much  used  as  a  fertilizer.     The 
reaction  is : 

Ca3(P04)2  +2H2S04  -^CaH4(P04)2  +2CaSO4 

The  solution  of  the  acid  calcium  phosphate, 
CaH4(PO4)2,  is  filtered  from  the  insoluble  calcium 
sulfate,  CaSO4,  evaporated  to  dry  ness,  and  the 
product  strongly  heated.  Water  is  thus  driven  off 
and  calcium  metaphosphate  formed : 

CaH4(PO4)2  ->Ca(PO3)2  +  2H2O 

This  is  mixed  with  charcoal  and  distilled  in  clay 
retorts  at  a  very  high  temperature.  The  phos- 
phorus formed  vaporizes  and  is  condensed  into  a 
liquid  under  warm  water  in  a  receiver. 

3  Ca(PO3)2  +  loC  — >  P4  +  Ca3(PO4)2  +  icCO 

The  product  is  purified  by  redistillation  or  by 
treatment  with  a  solution  containing  sulfuric  acid 
and  potassium  dichromate.  It  is  then  filtered 
through  canvas  and  cast  into  sticks. 

ELECTRO-CHEMICAL  PROCESS.  Natural  calcium  phos- 
phate is  intimately  mixed  with  carbon  and  sand,  and 
placed  in  a  retort-like  furnace  heated  inside  by  a  pow- 
erful electric  current  passing  between  carbon  elec- 
trodes. The  phosphorus  distills  off  and  is  condensed 
under  water. 

284.  Properties.      Physical.      (Table  I.,  Appen- 
dix D.)     Phosphorus,  when  freshly  prepared,  is  a 
translucent,  almost  colorless,  waxy  solid.     It  loses 


238  Elementary  Chemistry 

its  translucency,  however,  even  in  the  dark,  and 
when  exposed  to  light  turns  darker  and  darker  in 
color ;  an  allotropic  modification  (red  or  amorphous 
phosphorus)  is  formed.  It  is  somewhat  volatile  at 
ordinary  temperatures.  Its  vapor  density  is  62, 
which  shows  that  its  molecule  consists  of  four 
atoms,  or  is  tetratomic.  At  temperatures  above 
T, 000°  this  tetratomic  molecule  begins  to  dissoci- 
ate. Phosphorus  is  insoluble  in  water,  but  very 
soluble  in  carbon  bisulfid. 

Chemical.  Phosphorus  takes  fire  very  readily, 
and  is  hence  preserved  and  handled  under  water, 
which  protects  it  from  the  oxygen  of  the  air.  It 
burns  to  white  phosphorus  pentoxid,  P2O5.  It 
combines  with  the  halogens  even  at  ordinary  tem- 
peratures, and  with  many  other  elements;  its 
metallic  compounds  are  called  .  phosphids.  It  is 
very  poisonous,  and  persons  engaged  in  handling 
it,  in  its  manufacture,  or  in  that  of  matches,  are 
liable  to  be  attacked  by  serious  diseases  of  the  nose 
and  jaw. 

285.  Red  Phosphorus.     If  waxy  phosphorus  be 
heated  with  exclusion  of  air  or  oxygen  to  about 
250°,  it  changes  into  a  dark  red,  amorphous  mass. 
This  allotropic  form  has  no  odor,  is  insoluble  in 
carbon  bisulfid,  is  not  phosphorescent,  is  not  poi- 
sonous, and  has  a  rather  high  kindling  point.   When 
heated  above  300°  it  changes  back  into  the  ordinary 
form. 

286.  Uses.     Phosphorus  is  used  in  the  manu- 
facture of  matches  and  vermin  poisons.    Phosphates 
are  employed  in  fertilizers,  medicines,  and  some 
baking  powders. 


Phosphorus,  Arsenic,  Antimony,  Bismuth        239 

MATCHES.  Matches  consist  of  light  wood  sticks 
tipped  with  waxy  phosphorus  mixed  with  certain  sub- 
stances that  yield  oxygen  readily  when  heated.  Phos- 
phorus, together  with  lead  dioxid,  potassium  nitrate  or 
chlorate,  or  mixtures  of  these  compounds,  is  ground  up 
under  water  containing  a  little  gum.  The  ends  of  the 
match  sticks,  previously  coated  with  sulfur  or  paraffin, 
are  pressed  into  this  mixture  and  then  dipped  into  a  solu- 
tion of  gum  and  shellac  to  protect  the  phosphorus  from 
the  oxygen  of  the  air.  When  such  a  match  is  rubbed 
over  a  rough  surface,  the  gummy  coating  is  scratched 
off,  and  the  heat  due  to  the  friction  is  sufficient  to  set  on 
fire  the  phosphorus  which  burns  at  the  expense  of  the 
oxygen  in  the  other  ingredients.  The  sulfur  or  paraffin 
is  ignited  and  then  the  wood. 

"  Safety "  or  Swedish  matches  do  not  contain  any 
phosphorus  and  hence  are  not  poisonous,  and  do  not 
take  fire  from  friction  except  on  a  prepared  surface 
consisting  of  a  mixture  of  red  phosphorus,  fine  sand,  and 
gum,  applied  usually  to  the  sides  of  the  boxes  in  which 
the  matches  are  packed.  These  matches  are  tipped 
with  a  very  combustible  compound,  antimonious  sulfid, 
Sb2S3,  mixed  with  potassium  chlorate  and  dichromate 
and  red  lead.  The  friction  on  the  prepared  surface 
raises  the  temperature  enough  to  ignite  the  red  phos- 
phorus which,  while  it  does  not  burn  in  the  surface,  sets 
on  fire  the  combustible  material  on  the  stick. 


ARSENIC 

HISTORICAL  NOTE.  The  sulfid  ores  of  arsenic  have 
been  known  from  the  earliest  times,  and  the  alchemists 
knew  how  to  prepare  the  white  oxid  by  roasting  these 
ores.  This  oxid  was  long  called  arsenic,  and  it  was  not 
until  towards  the  end  of  the  eighteenth  century  that  it 
was  proved  to  be  a  compound  of  arsenic  and  oxygen. 

287.  Occurrence.  Arsenic  occurs  free  in  small 
quantities  in  a  few  places.  Its  main  natural  com- 
pounds are  arscnopyritc,  FeSAs,  realgar,  As2S2,  and 
orpiment,  As2S3o 


240  Elementary  Chemistry 

288.  Preparation.     Arsenopyrite   is   heated   in 
long  earthenware  retorts,  placed  horizontally  and 
fitted    with    earthenware    receivers.       The    pyrite 
decomposes : 

2  FeSAs  — »  2  As  +  2  FeS 

The  arsenic  volatilizes  and  condenses  in  the  receiv- 
ers as  a  compact  mass  and  is  purified  by  distillation. 
It  may  also  be  prepared  by  heating  arsenious  oxid 
with  charcoal : 

As4O6  +  6C  — >  4 As  +  6CO 

289.  Properties.     Physical.    (Table  I.,  Appendix 
D.)   Free  arsenic  resembles  metals  in  being  opaque, 
rather  heavy,  and  of  a  metallic  luster.     It  is  steel 
gray  in  color,  very  brittle,  and  a  good  conductor  of 
heat  and  electricity.     It  begins  to  sublime  at  about 
1 00°,  producing   a   yellow,  ill-smelling  vapor,  the 
vapor  density  of  which  is  about  300  =  (4  X  75).     Its 
molecule  consists  of  four  atoms  and  its  formula  is 
As4.     At  high  temperatures  the  As4  molecules  dis- 
sociate into  As  2  molecules. 

Chemical.  When  heated  in  oxygen  to  about  180°, 
arsenic  burns  with  a  bright  bluish-white  flame, 
forming  arsenious  oxid,  As4O6.  It  combines  readily 
with  the  halogens. 

290.  Uses.     Arsenic  in  small  proportion  forms 
with  lead  an  alloy  which  is  more  fusible  and  harder 
than  lead.     This  alloy  is  used  in  making  shot. 

ANTIMONY 

HISTORICAL  NOTE.  Antimony  was  investigated  with 
great  care  in  the  fifteenth  century  by  a  monk,  Basil 
Valentine,  who  published  his  results  in  a  book  bearing 
the  title  of  The  Triumphal  Chariot  of  Antimony. 


Phosphorus,  Arsenic,  Antimony,  Bismuth        241 

291.  Occurrence.     Antimony  is  found  in  small 
amounts  in  a  few  places,  but  it  is  generally  obtained 
from  its  mineral,  stibnitc  or  gray  antimony  ore,  Sb2S3. 

292.  Preparation.      I.     Stibnite  is  roasted,  and 
the  resulting  oxid  reduced  with  carbon : 

Sb2S3  +  502->     Sb204  +3S02 
Sb2O4  +  4C    -»2Sb          +4CO 

II.  Stibnite  is  heated  with  scrap  iron  in  plum- 
bago crucibles.  The  sulfur  leaves  the  antimony  to 
unite  with  the  iron,  and  as  the  molten  antimony  is 
heavier  than,  and  does  not  mix  with  the  iron  sulfid, 
it  sinks  to  the  bottom  and  may  there  be  drawn  off: 
3  Fe  +  Sb2S3  ->  3  FeS  +  2  Sb 

293.  Properties.     Physical.    (Table  I.,  Appendix 
D.)    Antimony  is  a  bluish-white  solid  with  a  brilliant 
metallic  luster,  and   does   not  tarnish  at  ordinary 
temperatures.     It  expands  at  the  moment  of  solidi- 
fication, and  is  on  that  account  made  one  of  the 
ingredients  of  type  metal,  to  which  it  imparts  the 
property  of  taking  sharp  castings.     It  is  so  brittle 
as  to  be  easily  pulverized.     Its  gaseous  molecule 
has  the  formula  Sb2. 

Chemical.  Antimony  burns  in  the  air  with  a 
white  flame,  yielding  dense  fumes  of  antimonious 
oxid,  Sb2O4,  and  combines  readily  with  the  halo- 
gens. Dilute  sulfuric  and  hydrochloric  acid  are 
without  action  upon  it,  while  the  concentrated 
acids  convert  it  into  the  sulfate  and  chlorid,  respec- 
tively. It  is  oxidized  by  nitric  acid. 

294.  Uses.     Antimony  is  chiefly  employed  in 
making  certain  alloys,  such  as  type  metal,  Britannia 
metal,  white  metal,  and  Babbitt  metal. 


242  Elementary  Chemistry 

BISMUTH 

HISTORICAL  NOTE.  Although  bismuth  has  been 
known  since  the  third  century,  it  was  confounded  with 
antimony,  and  it  was  not  until  the  middle  of  the 
eighteenth  century  that  its  true  nature  and  properties 
were  recognized. 

295.  Occurrence.     Bismuth  occurs  native  in  the 
veins  of  certain  crystalline  rocks,  and  most  of  the 
commercial   supply  is  obtained  from  this  source. 
Its   oxid,   Bi2O3    (bismuth  ochre],  and   sulfid,   Bi2S3 
(bismutkinite),  are  also  found. 

296.  Preparation.     Native  bisrnuth  is  heated  in 
inclined  iron  pipes.     The  bismuth  melts  and  runs 
off,  leaving  most  of  the  impurities  behind.     Such  a 
process  is  called  "  liquation." 

297.  Properties.    Physical.    (Table  I.,  Appendix 
D.)     Bismuth  is  a  lustrous  white  metal  with  a  red- 
dish tinge.    It  is  brittle  and  but  slightly  ductile  and 
malleable. 

Chemical.  Bismuth  burns  with  a  bluish  flame,  and 
combines  readily  with  the  halogens.  It  is  insoluble 
in  dilute  hydrochloric  and  sulfuric  acid,  but  easily 
soluble  in  nitric  acid  and  hot  concentrated  acids. 

298.  Uses.     Bismuth  forms  valuable  alloys  with 
other  metals,  imparting  to  them  hardness  and  fusi- 
bility.    Wood's  metal  and  Rose's  metal  are  alloys 
which  melt  below  100°. 

OXYGEN  COMPOUNDS 

299.  The  Oxids.    Phosphorus,  arsenic,  antimony, 
and  bismuth  each  form  several  oxids,  the  most  im- 
portant of  which  are  the  trioxids  and  pentoxids, 
corresponding  to  the  general  formulas  M2O3  and 
M2OS,  where  M  denotes  any  one  of  the  elements. 


Phosphorus,  Arsenic,  Antimony,  Bismuth        243 

The  oxids  are  white  or  light  yellow  powders,  and 
most  of  them  combine  with  water  to  form  acids. 

300.  Phosphorus  Trioxid,  P2O3.      Phosphorus 
trioxid   is    formed    by   burning    phosphorus  in    a 
limited  supply  of   oxygen.     It  is  a  white  powder, 
smelling  like  garlic,  and  soluble  in  water. 

301.  Phosphorus  Pentoxid,  P2OS.     Phosphorus 
pentoxid  is  prepared  by  burning  phosphorus  in  an 
abundance  of  oxygen.    It  is  a  soft,  light,  white  pow- 
der, very  soluble  in  water.     It  absorbs  water  from 
gases  eagerly,  and  hence  is  used  as  a  drying  agent. 

302.  Arsenious  Oxid  or  Arsenic  Trioxid,  As4O6. 
Arsenious  oxid  or  arsenic  trioxid  is  obtained  as  a  by- 
product in  the  roasting  of  certain  arsenical  pyrites. 
It  is  a  white  powder,  which,  when  sublimed,  yields 
glass-like  masses  (the  vitreous  modification).     It  is 
somewhat  soluble  in  water,  quite  so  in  dilute  hydro- 
chloric acid  and  sodium  hydroxid  solutions. 

Arsenic  trioxid,  commonly  known  as  white  arsenic, 
or  simply  arsenic,  is  the  most  abundant  commercial 
compound  of  arsenic.  It  has  a  slightly  sweetish 
taste,  and  is  very  poisonous,  if  not  more  than  0.02  #• 
be  taken.  Larger  doses  act  as  an  emetic,  while  very 
small  doses  act  as  a  tonic.  The  antidote  is  freshly 
prepared  ferric  hydroxid  or  magnesia.  At  tempera- 
tures from  200°  to  above  700°  the  molecule  As4O6 
dissociates  into  As2O3  molecules. 

ARSENIC  OXID  OR  PENTOXID,  As2Os.  Arsenic  oxid  is 
formed  by  heating  arsenious  oxid  with  strong  nitric  acid: 

As2O3  +  2  HNO3  — >  As2O5  +  NO  +  NO2  +  H2O 

The  products  of  the  reaction  when  heated  to  about 
300°  yield  the  pure  pentoxid  ;  when  to  a  red  heat,  the 
trioxid  and  oxygen  result. 


244  Elementary  Chemistry 

ANTIMONY  TRIOXID,  Sb2O3.  Antimony  trioxid  results 
when  antimony  is  oxidized  with  dilute  nitric  acid.  It  is 
a  white,  almost  insoluble  powder. 

ANTIMONY  PENTOXID,  Sb2Os.  Antimony  pentoxid  is 
obtained  by  oxidizing  antimony  with  strong  nitric  acid. 
It  is  a  light  yellow  powder,  slightly  soluble  in  water. 

ANTIMONY  TETROXID,  Sb2O4.  Antimony  tetroxid  is 
formed  by  heating  either  the  trioxid  or  the  pentoxid  in 
air.  It  is  a  white  powder,  insoluble  in  water. 

BISMUTH  OXIDS.  Of  the  four  oxids  of  bismuth 
known,  Bi2O2,  Bi2O3,  Bi2O4,  Bi2O5,  the  trioxid  is  the 
most  important.  It  is  a  yellow  powder,  used  in  making 
some  sorts  of  glass. 

ARSENIC  SULFIDS.  Two  sulfids  of  arsenic  are  found 
as  minerals,  realgar,  As2S2,  and  orpiment,  As2S3. 
Artificial  realgar  may  be  made  by  subliming  a  mixture 
of  arsenical  and  iron  pyrites.  .  It  is  a  red  glassy  mass 
used  as  a  pigment.  By  subliming  a  mixture  of  arse- 
nious  oxid  and  sulfur,  artificial  orpiment,  known  as 
"  King's  yellow,"  is  obtained.  The  trisulfid  may  also 
be  prepared  by  precipitating  a  solution  of  arsenic  by 
hydrogen  sulfid.  Arsenic  pentasulfid,  As2S5,  is  obtained 
by  fusing  the  trisulfid  and  sulfur  together. 

ANTIMONY  SULFIDS.  Antimony  trisulfid,  Sb2S3, 
occurs  in  nature  as  the  mineral  stibnite,  and  may  be 
prepared  by  passing  hydrogen  sulfid  into  a  solution  of 
antimony  trichlorid ;  it  is  precipitated  as  an  orange- 
yellow  powder,  coluble  in  solutions  of  alkalin  sulfids. 
The  pentasulfid  is  formed  by  precipitating  a  solution  of 
antimony  pentachlorid,  SbCl5,  with  hydrogen  sulfid.  It 
is  dark  orange  in  color  and  is  soluble  in  alkalin  sulfids. 

BISMUTH  TRISULFID,  Bi2S3.  Bismuth  trisulfid  is  the 
only  sulfid  of  bismuth,  and  occurs  as  the  mineral,  bis- 
muth glance.  It  is  formed  as  an  almost  black  precipi- 
tate when  hydrogen  sulfid  is  passed  into  a  solutio-n  of  a 
bismuth  salt. 

HYDROGEN  COMPOUNDS 

Arsenic,  antimony,  and  phosphorus  unite  with 
hydrogen  to  form  gaseous  compounds  of  consti- 
tution similar  to  that  of  ammonia.  They  are  all 


PliospJiorns,  Arsenic,  Antimony,  BismutJi         245 

colorless,  poisonous  gases,  with  a  very  disagreeable 
odor,  and  are  but  slightly  soluble  in  water. 

303.  Phosphin,  PH3.     (Hydrogen  Phosphid,  Phos- 
pJioretted  Hydrogen^]     Phosphin  is  made  by  heating 
phosphorus  with  a  strong   solution   of   potassium 
hydroxid.    A  small  amount  of  a  liquid  compound  of 
phosphorus  and  hydrogen,  P2H4,  is  also  formed,  and 
the  mixture  burns  on  coming  in  contact  with  the  air. 
If  the  P2H4  be  removed  by  passing  the  mixture 
through  a  tube  surrounded  with  a  freezing  mixture, 
the  pure  PH3  is  found  not  to  be  spontaneously  com- 
bustible.    Phosphin  may  also  be  prepared  by  the 
action  of  water  on  calcium  phosphid. 

ARSIN,  AsH3,  HYDROGEN  ARSENID.  (Arseniuretted 
Hydrogen.)  Arsin  is  formed  whenever  nascent  hydrogen 
can  react  upon  any  soluble  arsenical  compound.  It  is 
readily  decomposed  by  heat  into  hydrogen  and  arsenic. 

STIBIN,  SbH3,  HYDROGEN  ANTIMONID.  (Antimoniu- 
retted  Hydrogen.}  Stibin  is  made  like  arsin,  by  substi- 
tuting any  soluble  compound  of  antimony. 

HALOGEN   COMPOUNDS 

304.  Phosphorous  Chlorids.     Phosphorous  chlo- 
rids  are  prepared  by  passing  a  current  of  dry  chlorin 
over  phosphorus.     At  first  the  trichlorid,  PC13,  a 
colorless  liquid,  forms,  but  as   the   action   of  the 
chlorin  continues,  the  pentachlorid,  PC15,  a  yellow 
solid,  appears.     The  pentachlorid  decomposes  into 
the  trichlorid  and  chlorin  when  heated.     The  bro- 
mids  and  iodids  of  phosphorus  are  quite  similar  to 
the  chlorids. 

THE  HALOGEN  COMPOUNDS  OF  ARSENIC,  ANTIMONY, 
AND  BISMUTH.  The  halogen  compounds  of  arsenic,  anti- 
mony, and  bismuth  resemble  in  modes  of  preparation, 
properties,  and  reactions  those  of  phosphorus. 


246  Elementary  Chemistry 

ACIDS   AND   SALTS 

305.  Hypophosphorous  Acid.  Hypophosphorous 
acid,  H3PO2,  is  prepared  as  follows:  Phosphorus  is 
boiled  with  a  solution  of  barium  hydroxid,  Ba(OH)2, 
whereby    phosphin    and    barium    hypophosphite, 
Ba(H2PO2)2,   are   formed.     Sulfuric   acid   is   then 
added  in  quantity  just  sufficient  to  precipitate  all 
the   barium   as   insoluble   barium   sulfate,    BaSO4, 
leaving  the  hypophosphorous  acid  in  solution : 

Ba(H2PO2)2  +  H2SO4  -»  BaSO4  +  2  H3PO2 

Hypophosphorous  acid  is  a  white,  crystalline  solid, 

melting  at   170°,  which,  when  strongly  heated,  is 

converted  into  phosphin  and  orthophosphoric  acid: 

2  H3PO2  — >  H3PO4  +  PH3 

Although  orthophosphoric  acid  contains  three  hy- 
drogen atoms,  but  one  is  replaceable  by  a  univalent 
base  or  basic  radical ;  it  acts  as  a  monobasic  acid. 

306.  Phosphorous  Acid,   H3  PO3   or  P(OH)3. 
Phosphorous  acid  is  formed  when  phosphorous  oxid 
is  dissolved  in  water : 

P203  +  3H20->2H3P03 

or  when  phosphorous  trichlorid,  PC13,  is  acted  upon 
by  water: 

PC13  -f  3  H20  -»  P(OH)3  +  3  HC1 
The  formation  and  decomposition  of  phosphorus 
trichlorid  may  be  effected  simultaneously  by  pass- 
ing a  current  of  chlorin  into  melted  phosphorus 
under  hot  water.  Phosphorous  acid  is  a  white,  crys- 
talline solid,  melting  at  70°,  and  when  heated  decom- 
poses into  orthophosphoric  acid  and  phosphin : 

4HJPO,-»3H1P04  +  PH3 


Phosphorus,  Arsenic,  Antimony,  Bismuth        247 

Although  a  tribasic  acid,  its  tribasic  salts  are  un- 
stable. The  monobasic  and  dibasic  salts,  however, 
are  stable. 

Both  hypophosphorous  and  phosphorous  acids 
are  strong  reducing  agents;  they  absorb  oxygen 
eagerly  and  are  thus  converted  into  orthophos- 
phoric  acid. 

307.  Orthophosphoric    Acid,   H3PO4.      Ortho- 
phosphoric  acid  is  formed  when  phosphorus  pen- 
toxid  is  dissolved  in  boiling  water,  and  when  red 
phosphorus  is  oxidized  by  means  of  nitric  acid.     It 
is  a  white,  crystalline  solid,  melting  at  39°.    It  forms 
three  series  of  salts. 

308.  Pyrophosphoric  Acid,  H4P2O7.    Pyrophos- 
phoric  acid  is  obtained  from  orthophosphoric  acid 
by  heating  it  to  about  200°: 

2H3P04  --  H20-»H4P207 

309.  Metaphosphoric  Acid,  HPO3.     Metaphos- 
phoric  acid  may  be  obtained  by  heating  orthophos- 
phoric or  pyrophosphoric  acid  to  redness : 

H3P04  -  H20~>     HP03 
H4P2O7  --  H2O-*2HPO3 

It  is  a  glassy  solid  and  is  frequently  called  "  glacial 
phosphoric  acid."  In  solution  it  gradually  changes 
into  orthophosphoric  acid.  It  is  monobasic. 

310.  Phosphates    and    Their    Uses.      Soluble 
phosphates  are  essential  to  plant  life.     The  normal 
phosphate  of   calcium,  Ca3(PO4)2,  found  in  bone- 
ash  and  in  nature,  being  insoluble  in  water,  must 
first  be  converted  into  a  soluble  phosphate  that  it 
may  be  taken  up  by  plants.     By  the  action  of  dilute 
sulfuric  acid  the  normal  phosphate  is  converted  into 


248  Elementary  Cliemistry 

primary  calcium  phosphate,  Ca(H2PO4)2,  which  is 
soluble.  This  " superphosphate  of  lime"  is  much 
used  as  a  fertilizer  and  also  as  the  acid  constituent 
of  phosphatic  baking  powders. 

ARSENIC  ACIDS  AND  SALTS.  Arsenious  acids  have 
never  been  obtained,  but  three  series  of  arsenites  cor- 
responding to  three  hypothetical  acids,  ortho-arsenious 
acid,  H3AsO3,pyro-arsemous  acid,  H4As2O7,  and  meta- 
arsenious  acid,  HAsO3,  are  known.  All  but  the  alkalin 
arsenites  are  insoluble  in  water,  and  when  heated  are 
converted  into  arsenic  and  arsenates.  Arsenic  pen- 
toxid  dissolves  in  water,  forming  ortho-arsenic  acid, 
H3  AsO4.  By  heating  this  the/y/r0-  and  meta-arsenious 
acids,  H4As2O7  and  PIAsO3,  may  be  obtained.  All 
three  acids  are  crystalline  solids  and  form  salts  resem- 
bling those  of  the  corresponding  phosphorous  acids. 

ARSENIC  GREENS.  Two  arsenic  compounds  have  a 
bright  green  color  —  "  Scheele's  green,"  which  is  cop- 
per arsenite,  and  "  Schweinfurt's  green,"  a  mixture  of 
copper  arsenite  and  copper  acetate.  Both  are  known 
commercially  as  "Paris  green."  Their  use  as  dyes, 
which  was  formerly  quite  general,  has  been  discon- 
tinued because  of  their  poisonous  qualities  and  because 
harmless  substitutes  have  since  been  discovered.  The 
use  of  Paris  green  to  kill  potato  bugs  is  familiar. 

ANTIMONY  ACIDS  AND  SALTS.  Ortho-,  pyro-,  and 
meta-antimonic  acids,  H3SbO4,  H4Sb2O7,and  HvSbO3, 
are  known  and  resemble  the  corresponding  acids  of 
phosphorus  and  arsenic.  Meta-  and  pyro-antimoniates 
are  found,  but  no  ortho-antimoniates  are  known. 

Exercises 

1.  What  objection  is  there  to  the  use  of  arsenic  greens  for 
coloring  wall  papers? 

2.  Why  is  the  arsenic  vapor  molecule  supposed  to  consist  of 
four  atoms  ? 

j.     Why  is  not  phosphorus  used  for  illuminating  purposes  ? 

4.  What  class  of  substances  is  formed  by  the  action  of  water 
on  the  products  of  the  combustion  of  non-metals  ? 

5.  What  practical  value  have  low-melting  alloys  ? 


Phosphor  us  j  Arsenic,  Antimony,  Bismuth        249 

Problems 

/.  How  much  phosphorus  is  there  in  a  ton  of  bone-ash  if  68 
per  cent  of  the  ash  is  calcium  phosphate,  Ca3(PO4)2  ? 

2.  How  much  sulfur  dioxid  can  be  obtained  from  1,000  pounds 
of  stibnite,  Sb2S3  ? 

j>.  How  much  sulfur  is  combined  with  100^"-  of  realgar,  As2S2, 
and  of  orpiment,  As2S3,  respectively?  What  is  the  simplest  ratio 
of  these  amounts  ? 

4.  How  much  bone-ash  containing  68  per  cent  of  calcium 
phosphate,  Ca3(PO4)2,  must  be  employed  to  make  a  ton  of  the 
fertilizer,  superphosphate  of  lime  ? 

5.  If  one  million  matches  can  be  tipped  with  one  pound  of 
phosphorus,  how  much  phosphorus  does  your  family  use  in  a  year  ? 

6.  If  a  skeleton  weighs  21  pounds  and  contains  56  per  cent  of 
Ca3(PO4)2,  how  many  matches  can  be  tipped  with  the  phosphorus 
it  contains,  if  one  pound  of  phosphorus  serves  to  tip  a  million 
matches  ? 

7.  How  much  greater  is  the  percentage  of  phosphorus  in  cal- 
cium metaphosphate,  Ca(PO3)2,  than  in  calcium  orthophosphate, 
Ca3(POJ2  ? 

8.  At   236°  phosphorus  pentachlorid   dissociates   into   phos- 
phorus trichlorid  and  free  chlorin.     What  is  the  volume  of  the 
mixed  gases  when  10^-  of  the  pentachlorid  dissociate  ? 

g.  If  the  specific  gravity  of  phosphorus  is  i  84,  what  is  the 
weight  of  a  cylindrical  stick  of  it  2$cm.  long  and  o.$cm.  in 
diameter  ? 

10.  Calculate   the   percentage   composition  of  sodium   phos- 
phate, Na3PO4,  and  of  disodium  phosphate,  HNa2PO4. 

11.  What  is  the  loss  in  the  weight  of  a  stick  of  phosphorus 
which  has  been  employed  to  remove  the  oxygen  from  54. 8  c.c.  of 
air  at  20°  and  746  mm-  ? 

12.  Van  der  Plaats,  in  1885,  obtained  by  burning  18.5854^-  of 
phosphorus,  42.5840^-    of  phosphorus  pentoxid.     If  the   atomic 
weight  of  oxygen  is  taken  as  16.00,  what  is  the  atomic  weight  of 
phosphorus  ? 

ij.  Dumas,  in  1859,  decomposed  11.454^"-  of  phosphorus  tri- 
chlorid with  water,  precipitated  with  silver  nitrate,  and  found 
26.978^"-  of  silver  in  the  precipitate.  Write  the  equations  for  the 
reactions  involved  and  calculate  the  atomic  weight  of  phosphorus. 
The  atomic  weights  of  chlorin  and  silver  are  35.45  and  107.94, 
respectively. 


250  Elementary  Chemistry 

14.  Cooke,  in  1878,  precipitated  the  bromin  in  13.2659^-  of 
antimony  tribromid  as  silver  bromid,  obtaining  n.g^gig'-  of  silver. 
Taking  the  atomic  weights  of  bromin  and  silver  as  79.96  and 
107.94,  respectively,  calculate  the  atomic  weight  of  antimony. 

rj.  Schneider,  in  1856,  heated  antimony  sulfid,  Sb2S3,  in  a 
hydrogen  atmosphere  and  weighed  the  sulfur  given  off  as  well 
as  the  antimony.  The  results  of  three  determinations  were  : 

I  II  III 

Antimony,       1.49916        2.99091        5.85754 
Sulfur,    '         0.59890        1.19495        2.33959 

From  these  data  calculate  the  atomic  weight  of  antimony  ;  the 
atomic  weight  of  sulfur  is  32.06. 

16.  Dumas,  in  1859,  precipitated  the  chlorin  in  22.173  g>  of 
arsenic  trichlorid  with  silver  nitrate  solution  and  found  39. 597^- 
of  silver  in  the  silver  chlorid  thrown  down.  The  atomic  weights 
of  chlorin  and  silver  are  35.45  and  107.94,  respectively;  what  is  the 
atomic  weight  of  arsenic? 

77.  Marignac,  in  1884,  by  reducing  in  hydrogen  obtained  from 
29.5035^-  of  bismuth  oxid,  Bi2O3,  3.O44O<£"-  of  oxygen.  Calculate 
the  atomic  weight  of  bismuth,  taking  the  atomic  weight  of  oxygen 
as  16.00. 

18.  Marignac  also  converted  16.6450^"-  of  bismuth  oxid  into 
25.255i<?"-  of  bismuth  sulfate,  Bi2(SO4)3.  The  atomic  weight  of 
sulfur  is  32.06.  Calculate  that  of  bismuth. 


CHAPTER  XXIII 


THE   ALKALIN   EARTH    METALS  AND 
THEIR  COMPOUNDS 

The  metals  beryllium,  magnesium,  calcium,  stron- 
tium, and  barium  form  a  well-defined  group  of  ele- 
ments ;  the  properties  of  the  three  last  are  especially 
similar .  Beryllium,  formerly  called  glucinum  be- 
cause of  the  sweet  taste  of  some  of  its  salts,  is  rare 
and  resembles  magnesium  very  closely.  All  these 
metals  are  bivalent.  The  calcium,  strontium,  and 
barium  hydroxids  are  strong  bases  and  have  an 
earthy  appearance  ;  hence  the  name  of  alkalin  eartJis. 

311.  Occurrence.  The  alkalin  earth  metals  are 
never  found  free  in  nature,  but  certain  of  their  com- 
pounds, especially  the  sulfates  and  carbonates,  are 
very  abundant,  as  calcium  carbonate,  CaCO3  (calcite, 
marble,  and  limestone],  calcium  sulfate,  CaSO4  (sele- 
nite],  strontium  carbonate,  SrCO3  (strontianite], 
strontium  sulfate,  SrSO4  (celestite),  barium  carbon- 
ate, BaCO3  (witJierite),  barium  sulfate,  BaSO4 
(barite),  a  double  carbonate  of  calcium  and  magne- 
sium, MgCa(CO3)2  (dolomite).  Many  silicates,  such 
as  talc,  serpentine,  and  soapstone,  contain  magnesium, 
and  calcium  phosphate  is  common.  Magnesium 
chlorid,  MgCl2,  is  found  crystallized  with  potassium 
chlorid,  forming  carnallite,  MgCl2'KCl,  and  mag- 
nesium sulfate,  MgSO4,  occurs  in  certain  mineral 
waters. 

[251! 


252  Elementary  Chemistry 

312.  Preparation.     The  general  method  of  pre- 
paring the  alkalin  earth  metals  is  to  electrolyze,  their 
fused  chlorids.    Magnesium,  however,  was  formerly 
prepared  by  the  action  of  metallic  sodium  on  fused 
magnesium  chlorid : 

MgCl2  +  2  Na  — >  2  NaCl  +  Mg 

313.  Properties.    Physical.    (Table  I.,  Appendix 
D.)     Magnesium  is  of  a  silvery  white  color,  but  is 
usually  tarnished  with  a  coat  of  oxid.    Calcium  is 
also  silvery  white,  while  barium  and  strontium  have 
a  yellowish  tinge.     They  are  all  but  slightly  ductile 
and  malleable. 

Chemical.  The  alkalin  earth  metals  remain 
bright  in  dry  air,  but  in  moist  air  slowly  become 
converted  into  the  hydroxids.  When  heated,  they 
burn  vigorously,  magnesium  emitting  a  most  daz- 
zling light,  rich  in  rays  affecting  the  photographic 
plate.  Magnesium  decomposes  water  only  at  high 
temperatures,  while  the  other  metals  do  so  at  ordi- 
nary temperatures.  Magnesium  is  very  soluble  in 
most  acids,  setting  hydrogen  free,  and  when  heated 
in  nitrogen  combines  to  form  magnesium  nitrid. 

314.  Uses.     Metallic  magnesium  is  used  as  a 
source  of  light  ("  flashlight  ")  in  photography.     The 
other  metals  are  merely  chemical  curiosities. 

OXIDS  AND  HYDROXIDS 

315.  In  General.    The  oxids  of  the  alkalin  earth 
metals  are  often  named  according  to  the  old  no- 
menclature, thus:    MgO  is  magnesia;    SrO,  strontia ; 
BaO,  baryta  ;  calcium  oxid,  CaO,  is  quicklime.     They 
are   all   white,  earth-like,   almost   infusible   solids 
They  are  prepared  by  decomposing  their  carbonates 


Alkalin  EartJi  Metals  and  Their  Compounds     253 

or  nitrates  by  heat.  They  unite  with  water  to  form 
hydroxids,  the  solubility  and  alkalinity  of  which 
increase  with  the  molecular  weights. 

MAGNESIUM  OXID,  MgO.  Magnesium  oxid  is  a 
white,  bulky  powder  prepared  by  burning  magnesium 
or  calcining  its  carbonate.  It  is  known  in  commerce 
as  calcined  magnesia  or  magnesia  usta. 

MAGNESIUM  HYDROXID,  Mg(OH)2.  Magnesium 
hydroxid  is  ordinarily  prepared  by  precipitating  a  sol- 
uble magnesium  salt  with  either  sodium  hydroxid  or 
potassium  hydroxid. 

316.  Calcium  Oxid,  CaO.  (Quicklime^  Quick- 
lime is  formed  by  heating  to  redness  calcium  car- 
bonate, usually  in  the  form  of  limestone  or  chalk. 

Formerly  periodic  furnaces  (page  1 14)  were  used. 
A  cavity  was  scraped  out  on  the  side  of  a  limestone 
bluff,  an  arch  of  limestone  built  above  the  fire  pit, 
and  the  kiln  then  filled  up  with  blocks  of  limestone. 
A  fire  was  then  lighted  and  kept  burning  for  several 
days.  At  present,  however,  continuous  furnaces  are 
almost  exclusively  used  for  "burning"  limestone. 

Calcium  oxid  is  an  almost  infusible  solid,  and 
because  of  that  property  it  is  used  in  the  construc- 
tion of  electric  furnaces.  When  exposed  to  the  air 
it  becomes  "air-slaked,"  i.  e,,  it  combines  with  the 
moisture  and  carbon  dioxid  to  form  the  hydroxid 
and  ultimately  the  carbonate.  It  unites  with  water 
with  the  evolution  of  much  heat  to  produce  calcium 
hydroxid,  Ca(OH)2,  commonly  called  slaked  lime. 

Lime  is  extensively  used  in  making  mortar, 
cement,  bleaching  powder,  sodium  hydroxid,  and 
glass,  in  purifying  sugar  and  illuminating  gas,  in 
dyeing,  in  removing  the  hair  from  hides  before 
they  are  tanned,  and  as  a  fertilizer  and  disinfectant. 


254  Elementary  Chemistry 

317.  Calcium    Hydroxid,    Ca(OH)2.     (Slaked 
Lime}     Slaked  lime  is  a  white,  slightly  soluble  solid 
which,  when  dissolved,  gives  "lime  water."     If  an 
excess   of   the  finely  divided  solid   be  present,  it 
forms  a  suspension  popularly  known  as  "milk  of 
lime." 

THE  OXIDS  AND  HYDROXIDS  OF  STRONTIUM  AND 
BARIUM.  These  closely  resemble  in  properties  and 
modes  of  preparation  the  corresponding  compounds  of 
calcium. 

SOME   IMPORTANT   SALTS   OF   THE   ALKALIN 
EARTH    METALS 

318.  Magnesium  Chlorid,  MgCl2.     Magnesium 
chlorid  is  prepared  by  dissolving  magnesium,  its 
oxid  or  carbonate,  in  hydrochloric  acid.     From  this 
solution  colorless  crystals  are  obtained,  which,  when 
heated,  decompose  thus : 

MgCl2  +  H2O  -»  MgO  +  2  HC1 
But  if  ammonium  chlorid  be  added  to  the  solution, 
a  double  chlorid,  NH4C1  •  MgCl2,  is  produced  which 
can  be  evaporated  to  dryness  without  decomposition. 
Magnesium  chlorid  is  a  deliquescent,  white  solid. 

319.  Magnesium  Sulfate,  MgSO4.    (Epsom  Salts.} 
Magnesium  sulf ate  is  found  in  numerous  springs  and 
also  in  the  mineral,  kieserite.     It  forms  transparent 
crystals  of  a  very  bitter  taste.    It  is  used  in  medicine, 
as  a  fertilizer,  and  as  a  dressing  for  cotton  cloth. 

320.  Calcium  Chlorid,  CaCl2.    Calcium  chlorid  is 
obtained  in  large  amounts  as  a  by-product  of  several 
manufacturing   processes.     Calcium    carbonate    in 
any  of  its  forms  dissolves  in  hydrochloric  acid,  and 
by  concentration  of  the  solution,  colorless  crystals 
of  calcium  chlorid  combined  with  six  molecules  of 


Alkalin  Earth  Metals  and  Their  Compounds     255 

water  of  crystallization  are  obtained.  When  heated, 
the  water  of  crystallization  passes  off,  leaving  the 
salt  as  a  porous  mass,  which  attracts  water  with 
great  eagerness,  and  is  on  that  account  extensively 
used  as  a  drying  agent  for  gases  and  liquids. 

321.  Calcium   Fluorid,  CaF2.     Calcium   fluorid 
occurs   as   the   mineral,  fluorspar.      It   is   a  white, 
insoluble  solid,  and  is  the  source  of  nearly  all  fluo- 
rin  compounds. 

322.  Bleaching   Powder   or   Chlorid   of  Lime. 
Bleaching  powder  is  made  by  passing  chlorin  over 
freshly  slaked  lime.     The  chemical  reaction  as  well 
as  the  formula  of  the  product  is  as  yet  a  matter  of 
doubt.     Its  aqueous  solution,  however,  behaves  like 
a  solution  of  calcium  chlorid  and  calcium  hypochlo- 
rite.      It  is  a  white,  slightly  soluble  powder,  that 
decomposes  on  standing.      Its  bleaching  action  is 
brought  out  more  rapidly  by  some  agent,  as  an  acid 
or  even  certain  salts,  which  have  the  power  of  decom- 
posing it,  and  is  not  exercised  on  animal  substances. 
In  bleaching  cotton  or  linen  with  it,  the  goods  are 
cleansed  from  grease  and  oil,  and  steeped  in  a  solu- 
tion of  the  powder.     They  are  then  immersed  in 
dilute  sulfuric  acid,  whereby  the  chlorin  is  liberated 
and  the  bleaching  takes  place.     Chlorid  of  lime  is 
also  a  familiar  disinfectant. 

323.  Calcium  Carbonate,  CaCO3.     Calcium  car- 
bonate occurs  in  immense  deposits  in  many  parts  of 
the  earth  in  the  form  of  marble,  limestone,  chalk, 
and  coral.     The  shells  of  molluscs  and  other  lower 
forms  of  animals  consist  largely  of  this  substance, 
and  it  is  probable  that  the  natural  substances  named 
are  the  remains  of  these  animals  which  have,  during 


256  Elementary  Chemistry 

ages,  accumulated  at  the  bottoms  of  arms  of  the 
sea  which  have  since  dried  up  or  retreated.  These 
deposits,  from  pressure  and  elevation  of  temperature, 
have  in  the  course  of  time  been  converted  into  their 
present  forms.  The  original  animal  structure  can 
often  be  detected  in  the  hardest  marble  as  well  as 
in  the  softest  chalk.  Even  at  the  present  day  coral 
reefs  are  in  the  process  of  formation.  Calcium  car- 
bonate also  occurs  in  two  crystalline  forms,  arrago- 
nite  and  calc,  or  Iceland  spar;  the  latter  has  the 
property  of  doubly  refracting  light. 

DISSOCIATION  OF  CALCIUM  CARBONATE.  Calcium 
carbonate  dissociates  into  carbon  dioxid  and  lime: 

CaCO3  £±  CO2  +  CaO 

The  general  phenomenon  of  dissociation  was  first  made 
clear  by  a  study  of  this  simple  case  of  a  solid  dissoci- 
ating into  another  solid  and  a  gas.  It  was  found  that 
at  every  temperature  above  about  450°  a  certain  definite 
amount  of  carbon  dioxid  was  given  off,  which,  if  not 
allowed  to  escape  into  the  air,  exerted  a  certain  definite 
pressure.  Some  corresponding  values  of  temperature 
and  pressure  are  the  following  : 

Temperature:     547°      625°     740°       812°       865° 
Pressure :  27  mm-  56  mm-  255  mm-  765  mm-  1,333  mm' 

324.  Limestone.  Limestone  is  but  slightly  sol- 
uble in  water,  but  its  solubility  is  increased  when 
carbon  dioxid  is  present  in  the  water.  Subterranean 
waters  not  infrequently  hold  more  or  less  carbon 
dioxid  in  solution,  and  if  they  flow  over  limestone 
some  of  the  rock  passes  into  solution  and  is  thus 
carried  along  by  the  water.  Caves  are  formed  in  this 
way.  When  the  water  loses  its  carbon  dioxid,  or 
evaporates,  this  limestone  is  thrown  out  of  solution. 
In  this  way  the  columns  found  in  limestone  caves 


Alkalin  Eartli  Metals  and  Their  Compounds     2$7 

have  been  formed.  Water  charged  with  carbon 
dioxid  and  holding  limestone  in  solution  drips  from 
the  top  of  the  cave,  evaporates  somewhat,  and  thus 
loses  its  carbon  dioxid.  The  calcium  carbonate 
separates  out  and  in  the  course  of  time  forms  a 
column  projecting  downwards,  a  stalactite.  The 
water  dripping  to  the  floor  loses  more  carbon  dioxid 
and  hence  more  calcium  carbonate  separates  out  and 
a  corresponding  column  is  built  up,  a  stalagmite. 
Stalactite  and  stalagmite  may  ultimatelv  meet  and 
form  a  continuous  column. 

325.  Calcium  Sulfate,  CaSO4.     Calcium  sulfate 
is  very  abundant  in  nature ;  the  chief  natural  vari- 
ety is  gypsum,  which  is  used  in  making  plaster  of 
Paris  and  land  plaster,  a  fertilizer.     Alabaster  is  a 
granular  form  of  gypsum. 

326.  Plaster  of  Paris.     Plaster, of  Paris  is  pre- 
pared by  heating  gypsum  to  a  little  over  100°,  so  as 
to  expel  most  of  its  water  of  crystallization.    When 
mixed  with  water,  it  takes  up  its  water  of  crystalliza- 
tion and  the  result  is  a  white,  rather  hard  mass ;  the 
plaster  "  sets."    As  this  process  is  accompanied  with 
an  expansion  the  setting  plaster  makes  a  sharp  cast, 
and  it  is  widely  used  for  this  purpose.     Mixed  with 
lime  it  forms  the  "hard  finish  "  or  "putty  coat."     If 
heated  above  200°,  gypsum  loses  this  property  of 
recombining  with  its  water  of  crystallization  and  is 
valueless  for  making  plaster  casts. 

327.  "Hard   Water."     Most   spring   and   well 
waters  will  not  at  once  form  a  lather  with  soap,  but 
become  filled  with  curd-like  material  when  mixed 
with  a  soap  solution.     Such  waters  are  said  to  be 
"hard."    Certain  of  these  natural  waters  have  most 


258  Elementary  Chemistry 

of  their  hardness  removed  by  boiling,  and  they  are 
found  to  hold  calcium  carbonate  in  solution.  Other 
waters,  however,  do  not  lose  their  hardness  when 
boiled,  and  it  is  found  that  they  contain  calcium 
sulfate.  The  addition  of  sodium  carbonate  to  such 
hard  waters  precipitates  the  alkalin  earth  carbon- 
ates, and  thus  " softens"  the  water.  Water  contain- 
ing only  calcium  carbonate  is  said  to  be  "tempo- 
rarily hard/'  while  if  the  sulfate  of  calcium  be 
present,  it  is  said  to  be  "permanently  hard." 

CALCIUM  SULFID,  CaS.  Calcium  sulfid  is  produced 
by  reducing  calcium  sulfate  with  carbon  at  high  tem- 
peratures : 

CaSO4  +  4  C  — »  CaS  +  4  CO 

or  by  passing  hydrogen  sulfid  over  hot  slaked  lime  : 
Ca(OH)2  +  H2S  — >  CaS  +  2  H2O 

Calcium  sulfid  is  a  white,  insoluble  powder  which,  after 
exposure  to  light,  becomes  self-luminous  in  the  dark. 
Hence  it  is  used  in  making  luminous  paint. 

328.  Calcium  Phosphate,  Ca3(PO4)2.  Calcium 
phosphate  occurs  in  nature  as  the  mineral  phos- 
phorite, and  may  be  prepared  by  adding  sodium 
phosphate  to  a  solution  of  calcium  chlorid  contain- 
ing some  ammonia.  It  is  the  main  constituent  of 
the  ashes  of  bones.  It  reacts  with  nitric  and  hydro- 
chloric acids  to  form  soluble  compounds,  and  when 
treated  with  sulfuric  acid  is  decomposed,  thus : 

Ca3(PO4)2  +  2H2SO4  ->  2CaSO4  +  CaH4(PO4)2 

The  mixture  of  calcium  sulfate  and  mono-calcium 
phosphate  thus  obtained  is  extensively  used  as  a 
fertilizer  under  the  name  of  "superphosphate  of 
lime." 


Alkalin  Earth  Metals  and  Their  Compounds     259 

329.  The  Nitrates  of  the  Alkalin  Earth  Metals. 

The  nitrates  of  the  alkalin  earth  metals  are  pre- 
pared by  dissolving  their  carbonates  or  oxids  in 
dilute  nitric  acid.  They  are  all  white,  soluble  solids. 
When  strontium  nitrate,  Sr(NO3)2,  is  heated  with 
carbon  or  other  easily  combustible  substances,  the 
mixture  burns  with  a  red  flame.  Barium  nitrate, 
Ba(NO3)2,  under  similar  conditions,  gives  a  green 
flame.  These  mixtures  are,  on  this  account,  used 
in  the  manufacture  of  fireworks. 

330.  Barium  Sulfate,  BaSO4.     Barium    sulfate 
occurs  in  nature,  forming  large  crystals  with  a  high 
specific  gravity,  and  on  that  account  it  is  known  as 
heavy  spar  or  barytes.     It  is  formed  as  a  dense, 
white  precipitate  when  a  solution  of   barium  salt 
is  mixed  with  sulfuric  acid.     It  is  used  as  a  paint 
under  the  name  of  "  permanent  white." 

Exercises 

/.     How  is  magnesium  utilized  in  separating  argon  from  air  ? 

2.  What  class  of  substances  is  formed  by  the  action  of  water 
on  the  products  of  combustion  of  the  alkali  and  alkalin  earth 
metals  ? 

j».  By  what  chemical  tests  would  you  distinguish  marble  from 
fluorspar  ? 

4.  What  objections  are  there  to  the  use  of  hard  water  in  a 
steam  engine  and  in  a  laundry  ? 

j.  Devise  tests  for  ascertaining  the  composition  of  the  foun- 
dation stone  of  your  school  building. 

6.  If  the  cost  of  magnesia  and  lime  is  the  same,  which  is  the 
more  economical  for  liberating  ammonia  from  its  salts  ? 

Problems 

1.  How  many  grams  of  calcium  oxid  can  be  obtained  from 
1.5^-  of  marble  ? 

2.  What  is  the  percentage  composition  of  crystallized  barium 
chlorid,  Bad;,  +  2  H2O  ? 


260  Elementary  Chemistry 

j>.  How  much  BaCl2  +  2  H2O  is  required  to  precipitate  exactly 
as  BaSO4  the  sulfuric  acid  in  10^"-  of  Na2SO4  +  10  H2O  ? 

4.  Dumas,  in  1859,  found  as  the  result  of  sixteen  determinations 
that  6i.64O7.f-    of  barium  chlorid  gave  precipitates  with  silver 
nitrate  containing  63.9964^-  of  silver.     If  the  atomic  weights  of 
chlorin  and  silver  are  35.45  and  107.94,  respectively,  what  is  the 
atomic  weight  of  barium  ? 

5.  Heinrichson,   in   1902,    heated  31. 20762  <?"•    of   calcite    and 
obtained  17.49526^-  of  quicklime.     If  the  atomic  weights  of  oxy- 
gen and  carbon  are  16.000  and  12.001,  respectively,  what  is  the 
atomic  weight  of  calcium  ? 

6.  Richards,  in  1902,  found  that  9.00246^"-  of  calcium  chlorid, 
when  mixed  with  a  solution  of  silver  nitrate,  yielded  23. 2506^-  of  sil- 
ver chlorid.     If  the  atomic  weights  of  silver  and  chlorin  are  107.94 
and  35.45,  respectively,  what  is  the  atomic  weight  of  calcium  ? 

7.  Marignac,  in  1884,  converted  16.0263  ff-  of  magnesium  oxid 
into  47.801 5 <?"•  of  magnesium  sulfate.     Taking  the  atomic  weights 
of  oxygen  and  sulfur  as  16.00  and  32.06,  respectively,  calculate 
the  atomic  weight  of  magnesium. 

The  same  chemist  also  obtained  from  59. 4763 &•  of  magnesium 
sulfate,  i9.9379<£r-  of  magnesia.  Calculate  from  these  data  the 
atomic  weight  of  magnesium. 

8.  Scheerer,  in  1846,  obtained  3.8855<5r-  of  barium  sulfate  by 
adding  a  solution  of  barium  salt  to  a  solution  containing  2.oo65£"- 
of  magnesium  sulfate.     Assuming  the  atomic  weights  of  oxygen, 
sulfur,  and  barium  to  be  16.00,  32.06,  and  137.04,  calculate  the 
atomic  weight  of  magnesium. 

g.  25<?"-  of  magnesite,  MgCO3,  were  dissolved  in  dilute  sul- 
furic acid  and  the  solution  slowly  evaporated  at  20°.  After  \og- 
of  magnesium  sulfate  had  crystallized,  how  much  water  was  in 
the  mother  liquor,  the  solubility  of  magnesium  sulfate  at  20° 
being  20  per  cent  ? 

10.  Stromeyer,  in  1816,  on  dissolving  0.5^-  of  strontium  car 
bonate  in  acid  obtained  75. 54^-  of  carbon  dioxid  at  o°  and  760  ^w- 
Taking  the  weight  of  one  liter  of  the  gas  as  equal  to  1.966^-  and 
the  atomic  weights  of  oxygen  and  carbon  as  16.00  and  12.00, 
respectively,  calculate  the  atomic  weight  of  strontium. 


CHAPTER  XXIV 

BORON  AND  SILICON 

Boron  and  silicon  resemble  carbon  in  their 
physical  properties ;  their  compounds,  however,  are 
widely  different. 

BORON 

331.  Occurrence.     Boron  never  occurs  free;  its 
principal  compounds  are  boric  acid,  H3BO3,  and 
borax,  Na,B4O7;  the  former  is  found  in  Tuscany, 
the  latter  in  Tibet,  California,  and  Nevada. 

332.  Preparation.     The  reduction  of  boron  tri- 
oxid,  B2O3,  at  a  high  temperature,  by  means  of 
potassium,  sodium,  magnesium,  or  aluminum,  yields 
the  element  in  the  form  of  an  amorphous  brown 
powder. 

333.  Properties.      Amorphous  boron  dissolves 
in  molten  aluminum  and  on  cooling  separates  into 
crystals,  sometimes  transparent,  but  usually  brown 
in  color.      This  crystalline  variety,  which  always 
contains  some  carbon  and  aluminum,  closely  resem- 
bles the  diamond  in  hardness,  refractive  power,  and 
luster.     Boron  at  a  red  heat  combines  directly  with 
nitrogen,  forming  boron  nitrid,  BN,  a  light  powder, 
white  in  color  and  very  stable.      Boron  burns  to 
boron  trioxid,  B,O3. 

334.  Boric  Acid.     (Boracic  A cid.)   In  certain  vol- 
canic districts  in  Tuscany,  jets  of  steam,  containing 
boric  acid  in  small  amounts,  issue  from  the  ground 

[261] 


262  Elementary  Chemistry 

These  jets  of  steam  are  made  to  pass  into  tanks  of 
water,  which,  as  the  water  evaporates,  become  filled 
with  crystals  of  boric  acid.  This  has  a  glassy 
appearance  and  a  soapy  feel.  When  heated  to  about 
1 00°  it  loses  water  and  is  converted  into  metaboric 
acid,  HBO 2  : 

H3BO3  -  H2O->HBO2 

At  a  higher  temperature,  metaboric  acid  loses  water, 
and  tetraboric  acid,  H2B4O7,  is  produced: 

4HB02  -  H20-^H2B407 

And  at  a  higher  temperature  still,  boron  trioxid  is 
formed : 

H2B407  --  H20-^2B2O3 

If  a  solution  of  boric  acid  in  alcohol  be  ignited, 
the  flame  is  tinged  green  from  the  volatile  acid. 

Boric  acid  is  used  in  the  manufacture  of  enam- 
els and  glazes  for  pottery,  for  preserving  meat,  and 
as  an  antiseptic. 

335.  Borax.  When  solutions  of  boric  acid  and 
sodium  carbonate  are  heated  together,  carbon  dioxid 
is  evolved  and  borax  (sodium  tetraborate)  is  formed : 

4H3BO3  +  Na2CO3  -»  Na2B4O7  +  CO2  +  6H2O 

Borax  is  found  native  in  the  beds  of  dried-up 
lakes.  It  has  an  alkalin  taste  and  reaction,  and 
usually  crystallizes  with  ten  molecules  of  water. 
When  heated  it  swells  up  at  first  into  a  white 
porous  mass  from  loss  of  water  of  crystallization, 
and  finally  melts  to  a  clear,  glassy  liquid  which 
has  the  property  of  dissolving  many  metallic  com- 
pounds. As  these  ofttimes  impart  a  characteristic 
color  to  it,  this  behavior  is  applied  as  a  test  for 
certain  metals  in  chemical  analysis;  the  usual 


Boron  and  Silicon  263 

procedure  is  to  melt  borax  in  a  loop  of  platinum 
wire  so  as  to  form  a  transparent  globule,  and  to  add 
a  little  of  trie  compound  to  be  tested  to  the  bead. 
The  colors  which  the  beads  may  assume  depend 
upon  the  metal  in  the  tested  compound,  and  also  as 
to  whether  it  is  heated  in  the  oxidizing  or  reducing 
flame  of  a  blowpipe.  Acids  take  the  sodium  from 
borax  in  solution,  so  that  boric  acid  is  formed. 

Borax  is  used  in  the  manufacture  of  soap,  glass, 
varnish,  and  artificial  gems;  also  in  medicine  and 
in  the  laundry. 

SILICON  ^ 

Just  as  carbon  is  the  central  element  in  the  ani- 
mal and  vegetable  kingdoms,  so  js  this  very  similar 
element  central  in  the  mineral  kingdom.  Silicon 
compounds  are  very  numerous  and  widespread,  and 
silicon  is,  next  to  oxygen,  the  most  abundant  ele- 
ment known. 

336.  Occurrence.     Silicon  is  never  found  free. 
Its  compounds,  however,  are  almost  omnipresent; 
hundreds  of  minerals  and  rocks  are  composed  of 
silicates. 

337.  Preparation.      Silicon    is    obtained    when 
potassium  fluosilicate,  K2SiF6,  is  heated  with  so- 
dium or  potassium : 

K2SiF6  +  4K-^6KF  +  Si 

The  potassium  fluorid,  KF,  is  washed  out,  leaving 
the  silicon  as  an  amorphous,  brown  powder.  The 
crystalline  variety  may  be  obtained  by  adding  zinc 
or  aluminum  to  the  original  mixture  so  that  the 
silicon  may  crystallize  out  of  the  molten  metal.  It 
is  also  obtained  by  reducing  silicon  dioxid,  SiO2, 


264  Elementary  Chemistry 

with  carbon,  magnesium,  or  aluminum  in  an  elec- 
tric furnace. 

338.  Properties.     Silicon,  like  carbon,  presents 
three  allotropic  modifications,  amorphous,  graphi- 
toidal,  and  crystalline.     All  three  forms  are  quite 
stable  and  not  affected  by  the  action  of  the  usual 
reagents. 

339.  Silicon  Dioxid.    (Silica.}  Silicon,  unlike  car- 
bon, forms  but  one  oxid,  SiO2,  which  is  one  of  the 
most  abundant  and  important  of  substances.    Quartz, 
chalcedony,  jasper,  opal,  sandstone,  and  sand  are  nearly 
pure  silica.    It  enters  into  the  composition  of  several 
rocks,  and  is  found  in  the  stems  of  many  rushes  and 
grasses.     Diatomaccous  or  infusorial  earth  is  mainly 
silica  consisting  of  the  shells  of  microscopic  organ- 
isms called  diatoms.     Silica  melts  only  at  a  very 
high  temperature  and  is  insoluble  in  pure  water. 

340.  Quartz.     Quartz  makes  up  nearly  a  third 
of  the  weight  of  the  rocks  occurring  in  the  earth's 
crust.      It   usually    crystallizes   in   hard    six-sided 
prisms,  terminated  by  six-sided  pyramids.    Quartz 
containing  only  silica  is  as  transparent  as  glass,  and 
is  fashioned  into  gems  known  as  "-white  stones" 
and  into  "  pebble  "  lenses  for  spectacles  and  optical 
instruments.     It  is  also  melted  in  an  oxyhydrogen 
flame,  and   blown   into   beakers,  flasks,  and   other 
articles   for  use    in   chemical    laboratories.      Such 
"quartz   ware"   is    very    refractory    to   heat,    and 
stands    sudden    changes    of    temperature    without 
cracking.     Colored  violet  with  a  little  manganese 
dioxid,  it  forms  the  highly  prized  gem,  amethyst. 
False  topaz  is  quartz  colored  yellow,  and  smoky  quartz 
varies  in  color  from  nearly  white  to  quite  black. 


Boron  and  Silicon  265 

341.  Amorphous  Silica.    Alkalin  waters  dissolve 
not  inconsiderable  amounts  of  silica,  especially  un- 
der pressure  at  high  temperatures.    The  mouths  of 
geysers  have  been  built  up  of  the  silica  deposited 
by  the  alkalin  water  released   from  pressure  and 
cooled  on  escaping  into  the  air.     Agate,  chalcedony, 
and  opal  have  also  been  deposited  from  solution. 
Wood  decaying  under  water  holding  silica  in  solu- 
tion has  its  particles  replaced  by  silica,  so  that  in 
course  of  time  the  wood  turns  into  stone,  i.  e.,  petri- 
fies; the  structure  of  the  wood  is  perfectly  copied. 
Silica  is  insoluble  in  all  acids  except  hydrofluoric. 
When  fused  with  alkalin  hydroxids  or  carbonates, 
it  forms  the  silicates  used  in  glass-making. 

Sandstone  is  an  important  building  stone  and 
some  especially  hard  and  fine-grained  varieties  are 
made  into  whetstones  and  grindstones.  Sand  is 
used  in  making  mortar,  glass,  porcelain,  and  sand- 
paper. Infusorial  earth  is  used  to  polish  silver  (a 
common  commercial  article  is  "  electro-silicon "), 
and  in  making  dynamite,  some  cements,  and  refrac- 
tory brick. 

342.  Silicon  Hydrid,  SiH4.     Silicon  hydrid  is  a 
colorless  gas  obtained  by  the  action  of  hydrochloric 
acid  on  magnesium  silicid,  SiMg2.     As  thus  pre- 
pared, silicon  hydrid  is  spontaneously  inflammable, 
but  when  purified,  it  has  to  be  heated  before  it  will 
take  fire. 

343.  Silicon  Tetrachlorid,  SiCl4.    Silicon  tetra- 
chlorid  is  made  by  passing  chlorin  over  a  mixture 
of  silica  and  charcoal  heated  t»o  a  white  heat.     It  is 
a  volatile,  colorless  liquid,  totally  decomposed  by 
water  (§  346). 


266  Elementary  Chemistry 

344.  Silicon   Tetrafluorid,   SiF4.     Silicon  tetra- 
fluorid  is  a  gas  formed  by  the  action  of  hydrofluoric 
acid  on  silicon  and  its  compounds.     It  reacts  with 
water  very  vigorously,  but  is  only  partially  decom- 
posed, as  the  reaction  is  reversible. 

345.  Carborundum.      Carborundum    is    carbon 
silicid,  CSi,  and  is  formed  by  heating  to  a  very  high 
temperature  in  an  electric  furnace  a  mixture  of 
carbon,  sand,  and  salt.     The  salt  reacts  with  the 
metallic  impurities,  converting  them  into  chlorids 
which  escape  in  the  form  of  vapor.     The  silicon 
dioxid  is  reduced  and  combines  with  the  excess  of 
carbon  present  to  form  carborundum. 

Carborundum  is  almost  as  hard  as  the  diamond, 
and  is  extensively  used  for  grinding  and  polishing 
purposes ;  it  is  mixed  with  a  "  body  "  of  clay  and 
feldspar,  molded  into  the  desired  shapes,  such  as 
wheels  and  hones,  and  heated  to  a  temperature  high 
enough  for  the  mixture  to  become  vitrified,  i.  e.,  con- 
verted into  a  strongly  coherent  mass. 

346.  Silicic  Acids.     Silicon  chlorid  reacts  with 
water  thus : 

SiCl4  +  4H20  -»  Si(OH)4  +  4HC1 

The  normal  silicic  acid  thus  formed  easily  loses 
water  to  form  ordinary  silicic  acid,  H2SiO3,  and 
when  heated,  this  loses  water  and  is  converted  into 
silica,  SiO2.  Most  of  the  ordinary  silicates  are  de- 
rived from  the  acid  of  the  formula,  H2SiO3.  Thus, 
when  an  alkalin  carbonate  is  fused  with  sand,  the 
silicate  formed  corresponds  to  a  salt  derived  from 
an  acid  of  the  formula,  H2SiO3.  For  example : 

Si02  +  K2C03  ->  K2Si03  +  CO2 


Boron  and  Silicon  267 

Potassium  (and  also  sodium)  silicate  is  soluble  in 
water  and,  if  hydrochloric  acid  is  added  to  a  solu- 
tion of  such  a  silicate,  the  gelatinous  precipitate 
formed  is  probably  mainly  silicic  acid,  H2SiO3. 
Besides  these  there  are  many  other  silicic  acids  of 
more  complex  composition,  which  may  be  regarded 
as  derived  from  two  or  more  molecules  of  the  sim- 
pler ones  by  the  abstraction  of  water : 
-  2H2Si03  -- H20-^H2Si205 

3  H2SiO3  --  H2O  -»  H4Si3O8,  etc. 
Some  of  these  poly  silicic  acids  occur  in  nature ;  opal 
is  an  example.  Ordinary  silicic  acid  is  obtained  by 
adding  dilute  hydrochloric  acid  to  a  solution  of  an 
alkalin  silicate ;  it  presents  the  appearance  of  a 
white  gelatinous  mass. 

SILICATES.  Silicates  in  endless  variety  are  found  in 
nature.  Many  important  minerals  and  rocks  are  sili- 
cates, as  feldspar  and  mica,  which,  together  with  quartz, 
form  granite.  Slate,  clay,  and  soapstone  are  silicates. 
Only  silicates  of  the  alkali  metals  are  soluble  in  water. 

GLASS 

347.  Properties  of  Glass.  When  a  mixture  of 
sand,  limestone,  and  carbonate  of  soda  is  strongly 
heated,  it  fuses  to  a  clear  transparent  liquid  which 
on  cooling  does  not  solidify  at  a  certain  definite 
temperature,  but  remains  pasty  throughout  a  con- 
siderable range  of  temperature.  When  in  this  state 
it  may  be  given  any  desired  shape  which  is  retained 
when  it  becomes  cold  and  solid.  It  is  to  this  prop- 
erty and  to  its  transparency  that  glass  owes  its  value. 

MANUFACTURE.  The  mixture  destined  for  the  prepa- 
ration of  the  glass  is  placed  in  fire-clay  pots  and  heated 
in  a  circular  furnace.  As  the  temperature  rises  the 


268  Elementary  Chemistry 

mass  fuses  and  gives  off  carbon  dioxid,  finally  becoming 
quite  fluid.  The  workman  takes  out  the  glass  and  either 
blows  or  molds  it  into  the  desired  shape.  After  this  is 
done  the  objects  are  put  into  an  annealing  furnace  and 
are  allowed  to  cool  very  gradually.  Annealing  is  abso- 
lutely necessary,  as  the  glass  is  otherwise  brittle. 

Glass,  chemically  considered,  is  an  amorphous 
mixture  of  the  silicates  of  alkalin  and  alkalin  earth 
metals,  although  other  metals  may  also  be  present. 
The  properties  of  the  glass  depend  upon  the  nature 
of  its  ingredients  as  well  as  their  proportion.  So- 
dium makes  glass  brilliant  and  fusible,  but  gives  it 
a  greenish  tinge.  Potassium  imparts  no  color,  but 
renders  the  glass  less  brilliant  and  fusible.  Cal- 
cium increases  its  hardness  and  luster,  but  dimin- 
ishes its  fusibility,  while  lead  diminishes  its  hard- 
ness and  gives  heaviness  and  luster. 

WINDOW  GLASS.  Window  glass  is  made  from  white 
sand,  chalk  or  slaked  lime,  and  soda-ash  (sodium  car- 
bonate) or  salt-cake  (sodium  sulfate);  broken  glass, 
called  cutlet,  is  added  to  make  the  mixture  fuse  more 
readily.  This  glass  is  therefore  a  mixture  of  the  sili- 
cates of  sodium  and  calcium. 

BOTTLE  GLASS.  Bottle  glass  is  made  like  window 
glass,  but  the  materials  are  not  so  pure.  It  usually 
contains  some  iron,  which  imparts  to  it  a  green  color. 

FLINT  GLASS.  Flint  glass  —  so  called  because  pow- 
dered flint,  a  kind  of  amorphous  silica,  was  formerly  used 
in  manufacturing  it — is  a  mixture  of  potassium  and  lead 
silicates.  It  is  comparatively  soft  and  heavy,  and  has 
so  high  a  refracting  power  as  to  be  very  brilliant. 
Under  the  name  of  "  crystal "  it  is  used  in  making  the 
best  grades  of  lenses  and  table  glassware.  It  fuses 
more  readily  than  other  kinds  of  glass,  and  does  not 
resist  the  action  of  chemicals  well  enough  to  be  used  in 
the  laboratory.  If  it  contains  as  much  as  50  per  cent  of 
lead,  the  glass  is  called  "paste  "  and  is  used  in  making 
imitation  gems. 


Boron  and  Silicon  269 

BOHEMIAN  GLASS.  Bohemian  glass  is  a  mixture  of 
potassium  and  calcium  silicates.  It  is  hard,  melts  with 
difficulty,  and  is  but  slightly  affected  by  chemicals. 
Hence  it  is  well  suited  for  chemical  glassware. 

COLORING  GLASS.  Glass  is  colored  by  the  addition  of 
certain  metallic  oxids.  Thus,  cobalt  oxid  gives  a  dark 
blue  color,  manganese  dioxid  a  violet,  uranium  oxid  a 
yellow,  gold  oxid  a  ruby  red,  chromium  oxid  a  green. 
White  enamel  is  glass  rendered  white  and  opaque  by 
tin  or  antimony  oxid. 

PAINTING  ON  GLASS.  Painting  on  glass  is  done  by 
pigments  made  of  various  inorganic  substances  ground 
up  with  a  very  fusible  glass  and  turpentine.  After  the 
colors  have  dried,  sufficient  heat  is  applied  to  just  melt 
the  more  fusible  glass. 

348.  Mortar.     Mortar  is  made  by  mixing  slaked 
lime  (calcium  hydroxid),  Ca(OH)2,  with  sharp  sand 
and  water ;  if  hair  be  added,  the  product  is  plaster- 
ing.   The  hardening  of  the  mortar  is  an  imperfectly 
understood   process.      The   slaked   lime  combines 
with  the  carbon  dioxid  of  the  air  to  form  calcium 
carbonate.     The  sand  serves  mainly  to  make  the 
mass  porous  so  that  the  air  (and  the  CO2  in  it)  may 
penetrate   into  the   mortar.     The   hardening   is   a 
slow  process,  and  the  older  the  mortar  the  harder 
it  is  and  the  better  it  cements  the  bricks  and  stones 
together. 

349.  Hydraulic  Cements  or  Mortars.    Hydraulic 
cements   contain  clay  and  a  larger  proportion  of 
sand  than   ordinary  mortar.      They  harden    even 
under  water.     Portland  cement  is  made  by  heating 
three  parts  of  lime  to  one  of  clay  until  water  and 
carbon  dioxid  have  been  expelled,  and  then  pulver- 
izing the  mixture.     With  water  and  sand  it  forms 
a  stony  mass  which  becomes  harder,  stronger,  and 
more  durable  than  many  natural  building  stones. 


270  Elementary  Chemistry 

Exercises 

1.  How  can  you  determine  whether  a  given  crystal  is  quartz 
or  calcspar  ? 

2.  What  class  of  substances  must  be  present  in  subterranean 
waters  so  that  silica  may  be  held  in  solution  ?    What  substance 
is  required  to  keep  calcium  carbonate  in  solution  ?    Can  a  natural 
water  hold  in  solution  at  the  same  time  silica  and  calcium  carbo- 
nate?   Why? 

j.     What  are  the  products  obtained  by  heating  sodium  sulfate 
with  boracic  acid  ? 

4.  The  products  of  the  combustion  of  silicon  hydrid  are  silica 
and  water.     Write  the  balanced  equation  for  the  reaction. 

5.  Compare  the  properties  of  the  hydrogen  and  oxygen  com- 
pounds of  silicon  with  the  corresponding  compounds  of  carbon. 

Problems 

1.  What  is  the  percentage  composition  of  (a)  quartz,  (b)  borax? 

2.  How  many  grams  of  carbon  dioxid  are  evolved  when  100^"- 
of  borax  are  made  by  the  interaction  of  boric  acid  and  washing 
soda? 

j.    Which  contains  the  larger  percentage  of  boron,  boric  acid 
or  boron  trioxid  ? 

4.  Pelouze,  in  1845,  found  that  the  chlorin  in  2.621  g-  of  silicon 
tetrachlorid,  SiCl4,  united  with  6.6445.T-  of  silver.     If  the  atomic 
weight  of  silver  is  107.94,  calculate  that  of  silicon. 

5.  Thorpe  and  Young,  in   1887,  decomposed  95.52367  £•   of 
silicon  tetrabromid,    SiBr4,  by  action  with  water,  and  obtained 
i6.56868<f-  of  silica.     If  the  atomic  weights  of  oxygen  and  bromin 
are  16.00  and  79.96,  respectively,  find  the  atomic  weight  of  silicon. 


•^•T 

-     **>r 
ur  THE    ' 

UNIVERSITY 
or 


CHAPTER  XXV 

ZINC,  CADMIUM,  AND  MERCURY 

ZINC 

350.  Occurrence.     Zinc  is  found  only  in  combi- 
nation ;  its  principal  natural  compounds  are  the  car- 
bonate, ZnCO3  (smithsonite\  the  silicate,  H2Zn2SiO5 
(calamine),  the  sulfid,  ZnS  (sphalerite  or  zinc  blende], 
and  red  zinc  oxid,  ZnO  (zincite). 

351.  Metallurgy.     The  zinc  ores  are  converted 
into  zinc  oxid  by  roasting,  i.  e.,  heating  with  free 
access  of  air,  and  subsequent  reduction  with  char- 
coal. 

ZnCO3  — »  ZnO  +  CO2 
2  ZnS  +  3  O2  — »  2  ZnO  +  2  SO2 
ZnO  +  C  — »  Zn  +  CO 

The  zinc  vaporizes  and  then  at  first  condenses 
into  a  powder  ("  zinc  dust "),  but  finally  into  a  liquid 
which  is  drawn  off  and  cast  in  bars  called  spelter. 
It  contains  other  metals  and  is  refined  by  distilling 
it  in  earthenware  retorts. 

352.  Properties.     Physical.     (Table    I.,    Appen- 
dix D.)    Zinc  has  a  bluish-white  color  and  high  lus- 
ter.    At  prdinary  temperatures  it  is  rather  brittle ; 
when  heated  to  100  to  150°  it  becomes  so  malleable 
that  it  can  be  rolled  into  sheets,  while  above  200°  it 
is  brittle  enough  to  be  powdered. 

Chemical.  Zinc  is  inalterable  in  dry  air  at  ordi- 
nary temperatures,  but  in  moist  air  becomes  coated 
with  a  thin  covering  of  the  oxid.  When  heated  to 

[271] 


272  Elementary  Chemistry 

a  sufficiently  high  temperature,  it  burns  with  a 
bluish  flame.  Pure  zinc  is  but  slowly  attacked  by 
acids,  but  the  commercial  form  dissolves  readily 
both  in  acids  and  in  alkalis. 

VAPOR  DENSITY  OF  ZINC.  A  liter  of  zinc  vapor 
weighs  30.4 *"-,  i.  e.,  it  is  33.8  times  as  heavy  as  a  liter  of 
hydrogen.  As  its  specific  heat  shows  that  its  atomic 
weight  is  65.4,  it  follows  that  the  molecule  of  vaporized 
zinc  contains  but  one  atom.  The  same  is  true  of  cad- 
mium and  mercury. 

353.  Uses.     Zinc  is  extensively  used  in  electric 
batteries,  in  gutters,  bath  tubs,  and  to  protect  wood- 
work from  the  heat  of  a  stove.     Iron  dipped  into 
molten  zinc  becomes  covered  with  a  coating  of  the 
latter  metal,  which  protects  it  against  the  action  of 
the  weather;  this  is  known  as  "galvanized  iron"  and 
is  extensively  used  for  roofs,  pipes,  cornices,  and 
tanks.      Zinc   is  a   constituent  of  the  alloys,  brass 
(copper  and  zinc),  German  silver  (copper,  zinc,  and 
nickel),  and  bronze  (copper,  tin,  and  zinc). 

SOME  IMPORTANT  COMPOUNDS  OF  ZINC 

354.  Zinc  Oxid,  ZnO.     Zinc  oxid  is  obtained  by 
burning  zinc  or  by  heating  its  carbonate  or  nitrate. 
Familiar  names  for  it  are  "  flowers  of  zinc"  and 
."  philosopher's  wool."     When  hot  it  has  a  yellow 
color ;  when  cold,  white.     It  is  employed  as  a  paint 
under  the  name  of  zinc  white. 

355.  Zinc  Chlorid,  ZnCl2.     Zinc  chlorid  may  be 
obtained  by  dissolving  zinc  in  hydrochloric  acid  or 
distilling   a   mixture    of  zinc   sulfate   and    sodium 
chlorid :  ,    . 

ZnSO4  +  2NaCl  ->  Na2SO4  +  ZnCl2 


Zinc,  Cadmium,  and  Mercury  273 

Zinc  chlorid  is  a  white,  translucent  substance,  melt- 
ing easily  and  distilling  at  a  red  heat.  It  dissolves 
in  both  water  and  alcohol,  and  is  very  deliquescent. 
It  is  used  in  medicine  and  in  soldering.  Wood 
impregnated  with  it  is  preserved  from  decay. 

NOTE.  The  "cut  acid"  of  the  plumber  is  zinc  chlorid,  pre- 
pared by  dissolving  zinc  in  muriatic  (hydrochloric)  acid. 

356.  Zinc  Sulfate,   ZnSO4.     Zinc  sulfate  much 
resembles  magnesium  sulfate.     It  is  prepared  by 
roasting  zinc  sulfid  or  by  dissolving  zinc  in  sul- 
furic  acid.     It  is  a  white,  efflorescent  salt,  used  in 
medicine  and  in  dyeing. 

ZINC  SULFID,  ZnS.  Zinc  sulfid  separates  as  a  white 
precipitate  when  an  alkalin  sulfid  is  added  to  a  solution 
of  a  zinc  salt. 

CADMIUM 

357.  Occurrence  and  Properties.     Cadmium  is 
ordinarily  found  associated  with  zinc,  and  is  a  white, 
lustrous  metal  tarnishing  in  moist  air.    At  tempera- 
tures somewhat  above  its  melting  point  (315°)  it 
takes   fire   and  burns    with   a  brownish   flame   to 
cadmium  oxid,  CdO.     It  is  soft  enough  to  be  cut 
with  a  knife,  and  is  quite  ductile  and  malleable.     It 
is  an  important  constituent  of  the  amalgams  used 
by  dentists  for  filling  teeth. 

CADMIUM  SULFID,  CdS.  Cadmium  sulfid  is  precipi- 
tated as  a  bright  yellow  solid  when  hydrogen  sulfid  is 
passed  into  a  solution  of  a  cadmium  salt  ;  it  is  used  as 
a  paint. 

MERCURY 

358.  Occurrence.      Mercury   sometimes   occurs 
free  in  little  globules  in  certain  rocks,  but  is  princi- 
pally obtained  from  its  sulfur  ore,  cinnabar,  HgS.  . 

19 


274  Elementary  Chemistry 

359.  Preparation.    Cinnabar  is  roasted,  whereby 
mercury  and  sulfur  dioxid  are  formed;  the  sulfur 
•dioxid  passes  off  and  the  mercury  is  collected  in  a 
series   of   condensing   chambers,   filtered   through 
cloth,  and  distilled. 

360.  Properties.    (Table  I.,  Appendix  D.)    Mer- 
cury is  the  only  one  of  the  metals  which  is  liquid  at 
ordinary  temperatures.     It  is  silvery  white,  with  a 
brilliant  luster.     It  does  not  change  in  the  air  unless 
heated  to  its  boiling  point  (360°),  when  it  oxidizes 
to  mercuric  oxid,  HgO.     It  is  insoluble  in  hydro- 
chloric  acid   and   cold   sulfuric    acid.      It   reduces 
hot  sulfuric  acid  and  dissolves  in  nitric  acid.    With 
most  metals  it  forms  alloys,  called  amalgams ;  iron 
and  platinum  are  notable  exceptions. 

361.  Uses.     Mercury  is  extensively  used  in  mak- 
ing thermometers  and  barometers,  in  amalgamating 
the  zinc  plates  of  electrical  batteries,  and  in  the 
extraction  of  gold  and  silver  from  their  ores.     A 
tin  amalgam  is  employed  in  the  manufacture  of 
mirrors. 

SOME  IMPORTANT  COMPOUNDS  OF  MERCURY 

362.  Salts.     Mercury  forms  two  series  of  salts. 
In  mercurous  salts,  it  is  univalent;    in  mercuric, 
bivalent. 

363.  Mercuric  Oxid,  HgO.     Mercuric   oxid, 
which  is  also  called  red  oxid  of  mercury  and  red  pre- 
cipitate, forms  when  mercury  is  heated  to  its  boiling 
point.     It  is  black  when  hot,  and  either  red  and 
crystalline  or   yellow  and   amorphous  when  cold. 
At  high  temperatures  it  breaks  up  into  oxygen  and 
mercury  (§  30). 


Zinc,  Cadmium,  and  Mercury  275 

364.  Mercuric  Chlorid,  HgCl2.    (Corrosive  Subli- 
mated]    Corrosive  sublimate  is  made  by  subliming 
an  intimate  mixture  of  mercuric  sulfate  and  com- 
mon salt : 

HgSO4  +  2  NaCl  ->  Na2SO4  +  HgCl2 

It  is  a  white,  crystalline  solid,  soluble  in  water.  It 
is  very  poisonous  and  is  used  as  an  antiseptic. 

365.  Mercurous  Chlorid,  HgCl.   (Calomel^    Cal- 
omel  is  manufactured   by  subliming   an  intimate 
mixture. of  mercuric  chlorid  and  mercury: 

HgCl2  +  Hg  ->  Hg2Cl2  or  2  HgCl 

It  is  also  formed  when  any  soluble  chlorid  is  added 
to  a  solution  of  a  mercurous  salt.  It  is  a  heavy, 
white  solid,  insoluble  in  water.  It  is  used  exten- 
sively in  medicine. 

366.  Mercuric    Sulfid,    HgS.       Mercuric   sulfid 
occurs  in  Spain,  Austria,  and  California  as  the  min- 
eral, cinnabar.     It  is  the  most  important  ore  of  mer- 
cury and   furnishes   the   greater  part  of  mercury 
used.     It  may  be  prepared  by  rubbing  flowers  of 
sulfur  together  with  mercury  or  by  passing  hydro- 
gen sulfid  into  a  solution  of  a  mercury  salt,  when  it 
is  thrown  down  as  a  black  powder  which  turns  red 
when  sublimed.     It  is  used  as  a  pigment  under  the 
name  of  vermillwn. 

367.  Mercury    Nitrates.      Mercurous   Nitrate, 
HgNO3,  results  from  the  action  of  nitric  acid  on  an 
excess  of  mercury  at  ordinary  temperatures,  while 
mercuric  nitrate,  Hg(NO3)2,  is  formed  when  the  acid 
is  in  excess  and  the  reaction  is  made  to  take  place 
at  a  higher  temperature.      They  are  both  white, 
crystalline  solids. 


276  Elementary  Chemistry 

« 

Exercises 

1.  How  is  the  zinc  used  in  the  extraction  of  silver  from  lead 
"  recovered"  so  that  it  may  be  used  over  and  over  again  ? 

2,  Under  what  circumstances  are  paints  made  from  "zinc 
white"  preferable  to  white-lead  paints  ? 

j.  Suppose  a  deposit  of  an  ore  was  found,  an  analysis  of 
which  showed  it  to  be  mercury  oxid  mixed  with  some  sand  and 
light  earthy  materials.  What  metallurgical  process  would  you 
suggest  for  obtaining  the  mercury  in  a  pure  state  ? 

4.  What  are  the  properties  of  mercury  that  make  it  adapted 
for  use  in  (a)  thermometers,  (b)  barometers  ? 

5.  What  physical  properties   of  mercury  does  its  common 
name,  "  quicksilver,"  connote  ? 

Problems 

/.  What  is  the  specific  heat  of  cadmium  if  its  atomic  weight 
is  112? 

2.  How  much  (a)  corrosive  sublimate,  (b}  calomel  can  be 
obtained  from  100^-  of  mercurous  sulfate? 

j.  What  is  the  percentage  composition  of  zinc  silicate, 
Zn2Si04? 

4.  Van  der  Plaats,  in  1885,  dissolved  29.6754^-  of  zinc  in  dilute 
sulfuric  acid  and  obtained  5.0834  /•  of  hydrogen.    What  is  the  equiv- 
alent weight  of  zinc  ?    The  atomic  weight  ? 

5.  so.?"-  of  zinc  were  dissolved  in  dilute  sulfuric  acid  and  the 
solution  allowed  to  evaporate  slowly  at  10°.     If  the  solubility  of 
zinc  sulfate  at  10°  is  30  per  cent,  how  much  water  was  present  in 
the  mother  liquor  when  2O.T-  of  the  salt  had  crystallized  out  ? 

6.  Hauer,  in  1858,  found  by  heating  64.2051  <?••  of  cadmium 
sulfate,  CdSO4,  that  44. 4491 8-  of  cadmium  sulfid  were  left.     Tak- 
ing the  atomic  weights  of  oxygen  and  sulfur  as  16.00  and  32.06, 
respectively,  calculate  the  atomic  weight  of  cadmium. 

7.  Huntington,  in  1882,  added  silver  nitrate  to  a  solution  of 
cadmium  bromid,   CdBr2,   and  found  the  ratio  of  the  weights 
of   cadmium    bromid   taken    and    silver   bromid   formed    to    be 
23.3275  :  32.2098.     The  atomic  weights  of  silver  and  bromin  are 
107.94  and  79.96,  respectively;  calculate  the  atomic  weight  of  cad- 
mium. 

8.  How  much  sulfuric  acid  could  theoretically  be  obtained 
from  1,000^-  of  cinnabar,  HgS  ? 


Zinc,  Cadmium,  and  Mercury  277 

g.  Morse  and  Burton,  in  1888,  oxidized  16. 03161  £•  of  zinc  with 
nitric  acid,  obtaining  20.2608^-  of  zinc  oxid.  Calculate  the  atomic 
weight  of  zinc. 

10.  How  many  kilograms  of  mercury  can  be  obtained  from 
50^-  of  cinnabar  by  heating  in  a  furnace  whereby  the  sulfur 
burns  to  sulfur  dioxid,  and  the  mercury  vaporizes  and  is  after- 
ward condensed  ? 

//.  Erdmann  and  Marchand,  in  1844,  obtained  352. 4079^-  of 
mercury  by  heating  38o.5744<?"-  of  mercuric  oxid.  What  is  the 
atomic  weight  of  mercury  ? 

12.  Millon,  in  1846,  found  that  corrosive  sublimate  contained 
73.845  per  cent  of  mercury.  The  atomic  weight  of  chlorin  is 
35-45  5  what  is  that  of  mercury  ? 

/j.  How  many  liters  of  oxygen  at  20°  and  j^mm.  Can  be 
obtained  from  50^"-  of  mercuric  oxid  ? 

14.  Erdmann  and  Marchand,  in  1844,  heated  177.1664^-  of 
mercuric  sulfid  and  obtained  152.7450^"-  of  mercury.  The  atomic 
weight  of  sulfur  is  32.06  ;  what  is  that  of  mercury  ? 


CHAPTER  XXVI 


ALUMINUM 

368.  Occurrence.      Aluminum   does  not   occur 
free  in  nature,  but  in  combination  is  found  in  large 
quantities  and  very  widely  diffused.     Its  most  com- 
mon and  plentiful  compounds  contain  oxygen  and 
silicon.     Feldspar,  KAlSi3O8,  is  a  silicate  of  potas- 
sium and  aluminum..  Mica  is  a  general  name  applied 
to  mineral  silicates  of  aluminum,  potassium,  and 
magnesium.     Bauxite  is  a  mixture  of  the  hydrox- 
ids  of  aluminum  and  iron.     Cryolite  is  a  fluorid  of 
aluminum  and  sodium.      Pure   clay  or  kaolin  is  a 
hydrated  orthosilicate  of  aluminum,  Al  4  (SiO  4 )  3  -|- 
4  H2O,  and  is  white  ;  the  different  colors  of  ordinary 
clay  are  due  to  the  presence  of  other  compounds, 
those  of  iron  predominating. 

369.  Metallurgy.    Aluminum  was  first  prepared 
by    the    action    of   sodium   on   aluminum    chlorid, 
A1C13.     Electrolytic  methods,  however,  have  super- 
seded this  method.     Of  these,  several  have  been 
proposed,  but  the  most  successful  is  known  as  the 
"  Hall's  Process."    Iron  tanks  are  lined  with  carbon, 
forming  the  cathode,  while  large  carbon  rods  form 
the  anode.     The  electrolyte  is  aluminum  oxid  dis- 
solved in  a  melted  mixture  (fln.v]  of  cryolite.     The 
mixture  is  melted  and  kept  in  fusion  by  the  great 
heat  evolved  because  of  the  high  resistance  to  the 

[278] 


Aluminum 


279 


passage  of  the  electric  current  (Fig.  36).  The  alum- 
inum collects  in  liquid  form  at  the  bottom  of  the 
tanks,  while  the  oxygen  combines  with  the  carbon 
to  form  carbon  monoxid.  As  the  aluminum  oxid 
becomes  electrolyzed,  more  is  put  into  the  flux  from 
time  to  time.  The  cryolite  itself,  acting  merely  as 
a  solvent,  undergoes  no  change. 


Fig.    36 THE    ELECTRIC    FURNACE    USED    IN    PREPARING   ALUMINUM    BY     '  HALL'S 

PROCESS " 

370.  Properties.  Physical.  (Table  I.,  Appen- 
dix D.)  Aluminum  is  a  silvery  white  metal  of  about 
the  same  density  as  glass.  It  is  very  strong,  quite 
malleable,  but  not  very  ductile.  It  does  not  "work" 
well  in  a  lathe  and  is  hard  to  weld  or  solder.  It  is 
a  good  conductor  of  heat  and  electricity,  and  is  a 
serious  competitor  of  copper  in  electric  conductors. 

Chemical.-  Aluminum  is  not  affected  appreciably 
by  moist  or  dry  air,  even  when  carbon  dioxid, 
hydrogen  sulfid,  or  other  corrosive  gases  are  pres- 
ent. It  is  hardly  attacked  by  nitric  acid,  and  is  dis- 
solved but  slowly  by  sulfuric  acid.  Hydrochloric 
acid  and  the  fixed  alkalis  dissolve  it  readily. 

THERMOLYSIS.  Aluminum  reduces  many  oxids  with 
evolution  of  great  heat.  This  property  is  utilized  in  the 


280  Elementary  Chemistry 

preparation  of  certain  metals  and  is  also  being  applied 
in  the  welding  of  steel  rails.  The  ends  of  the  rails 
are  brought  together  and  covered  with  a  mixture  of 
iron  oxid,  sand,  and  aluminum  powder,  together  with  a 
cement  to  make  the  mixture  compact.  A  "  primer," 
consisting  of  a  mixture  of  substances  rich  in  oxygen, 
as  potassium  chlorate,  etc.,  and  a  piece  of  magnesium 
ribbon,  is  placed  in  the  above  mixture  and  the  ribbon 
ignited  with  a  match.  The  reaction  then  spreads 
through  the  entire  mass,  producing  heat  enough  to 
weld  the  rails  together. 

371.  Uses  and  Alloys.     Aluminum   is   coming 
more  and  more  into  general  use  in  the  form  of 
kitchen  utensils,  small  wares,  surgical  and  scientific 
instruments.     Aluminum  leaf  is  used  to  decorate 
book  covers  and  signs,  and  aluminum  powder  is 
applied  in  painting  many  metallic  objects,  such  as 
letter  boxes  and  radiators,  which  are  exposed  to 
heat  or  to  the  weather.     It  forms  many  valuable 
alloys.     Less    than    one    per   cent    added   to   steel 
greatly  improves  it.     Aluminum  bronze,  an  alloy  of 
copper  and  aluminum,  resembles  gold  in  appear- 
ance and  is  very  strong1  and  non-corrosive.     Magna- 
lium  is  an  alloy  of  aluminum  and  magnesium. 

SOME  IMPORTANT  COMPOUNDS  OF  ALUMINUM 

372.  Salts.     Aluminum  is  always  trivalent,  and 
forms  no  salts  with  very  weak  acids. 

SOURCE  OF  COMPOUNDS.  Aluminum  compounds  were 
formerly  prepared  from  alum  shale,  a  mixture  mainly  of 
the  silicates  of  aluminum  and  potassium  and  of  iron 
sulfid.  This  is  broken  up  into  small  pieces,  heaped  up 
with  coal  or  wood,  which  is  set  on  fire  and  allowed  to 
smolder  for  some  time.  The  product  is  then  spread  out 
and  exposed  to  the  weather  for  some  months.  The  sul- 
fur combined  with  the  iron  is  oxidized  to  sulfuric  acid, 


Alniniiniui  281 

which  decomposes  the  silicates.  The  final  products  are 
chiefly  the  sulfates  of  potassium,  aluminum,  and  iron. 
These  are  leached  out  and  allowed  to  crystallize  ;  the 
aluminum  and  potassium  sulfates  separate  ou-t  first  as 
alum. 

The  chief  sources  of  aluminum  compounds  nowadays 
are  bauxite  and  cryolite.  When  bauxite  is  heated  with 
sulfuric  acid,  a  mixture  of  aluminum  and  iron  sulfates  is 
obtained,  which  is  known  as  "alum  cake,"  and  is  exten- 
sively used  in  purifying  water  (page  41).  When  bauxite 
is  heated  with  soda  ash  soluble  sodium  aluminate  is 
formed,  the  solution  of  which,  when  separated  from  the 
insoluble  impurities  and  treated  with  carbon  dioxid  gas, 
gives  a  precipitate  of  fairly  pure  aluminum  hydroxid. 
The  sulfuric  acid  converts  this  into  the  sulfate  ;  the 
product  is  known  as  "concentrated  alum."  Cryolite 
also,  when  boiled  in  milk  of  lime,  forms  sodium  alumi- 
nate, from  which  "  concentrated  alum  "  may  be  obtained. 

373.  Alums.     Alums  are  double  sulfates   of   a 
trivalent  metal,  such  as  aluminum,  and  an  univalent 
metal,  such  as  potassium,  which  always  crystallize 
with  twenty-four  molecules  of  water.    The  formula 
of  ordinary  or  potash  alum  is  A12(SO4)3'  K2SO4  -f- 
24  H2O.    All  alums  are  soluble  in  water  and  have  a 
more  or  less  pronounced  astringent  taste.     Sodium 
alum,  A12(SO4)3-  NaSO4  +  24  H2O,  is  used  in  the 
manufacture  of  some  baking  powders.    Potash  alum 
is  used  in  dyeing  and  printing  cloth,  in  tanning  and 
paper  making,  in  purifying  water,  in  making  wood 
and  cloth  fireproof,  and  as  a  medicine. 

374.  Aluminum  Hydroxid,  A1(OH)3.  Aluminum 
hydroxid  is  precipitated  as  a  white,  gelatinous  mass 
when  ammonia  is  added  to  a  solution  of  any  alumi- 
num salts.     It  is  soluble  in  acids,  forming  the  cor- 
responding salts.     It  is  also  soluble  in  the  fixed 
alkalis,  forming  salts  called  aluminates,  in  which  the 


282  Elementary  Chemistry 

hydrogen  of  the  hydroxyl  is  replaced  by  alkali 
metal,  as  shown  in  the  formulas  for  potassium  and 
sodium  aluminates,  A1(OK)3  and  Al(ONa)3.  When 
aluminum  hydroxid  is  heated  it  loses  water,  and  a 
compound  of  the  formula,  HA1O3,  is  formed.  This 
acts  as  an  acid  and  forms  salts,  some  of  which  are 
minerals,  as  spinel,  which  is  magnesium  aluminate, 
Mg(AlO2)2.  When  heated  to  a  still  higher  temper- 
ature, aluminum  hydroxid  is  converted  into  alumi- 
num oxid. 

375.  Aluminum  Oxid,  A12O3  (alumina).  Alumi- 
num oxid  is  a  white  powder  insoluble  in  water.  It 
occurs  in  nature  as  corundum,  which  is  nearly  as  hard 
as  diamond.  An  impure  variety  is  emery,  much  used 
in  grinding  and  polishing.  The  ruby  is  crystallized 
alumina  colored  with  chromium  oxid,  while  the 
sapphire  is  colored  with  cobalt. 

The  ruby  and  the  sapphire  can  be  prepared  artifi- 
cially by  heating  aluminum  oxid  with  lead  oxid  in  a 
Hessian  crucible  to  a  bright  red  heat ;  a  little  potassium 
dichromate  or  cobalt  chlorid  is  added  to  give  the  charac- 
teristic color  of  the  ruby  or  sapphire,  respectively.  The 
silica  of  the  crucible  acting  on  the  compound  of  lead 
oxid  and  alumina  formed  sets  free  the  alumina  in  crys- 
tals closely  resembling  the  natural  gems. 

ALUM  TANNING.  When  water-soaked  hides  are 
placed  in  a  solution  of  potash  alum  containing  common 
salt,  alumina  is  deposited  in  the  fibers  of  the  skin  and 
serves  to  prevent  hardening.  The  skin  is  then  thoroughly 
rubbed  and  worked  with  fat,  yielding  a  strong  and 
pliable  leather.  Leather  for  kid  gloves  is  made  in  this 
way  from  the  skins  of  lambs  and  kids. 

MORDANTS.  In  dyeing  cloth,  especially  cotton,  it  is 
often  necessary  to  employ  a  mordant  to  fix  the  color 
and  make  it  fast.  The  cloth  is  first  saturated  with  the 
mordant  and,  when  dry,  is  dipped  into  a  solution  of  the 
coloring  matter.  This  reacts  with  the  mordant,  with 


A  lu  m  in  um  283 

the  result  that  the  solid  color  is  precipitated  right  in 
the  fiber  and  cannot  be  removed  by  washing.  Alumi- 
num acetate  and  sulfate,  as  well  as  alum,  are  much  used 
as  mordants. 

376.  Aluminum  Chlorid,  A1C13.    Aluminum 
chlorid  is  formed  by  the  action  of  hydrogen  chlorid 
on  aluminum  filings  heated  in  a  porcelain  or  glass 
tube.    The  white  powder  sublimes  from  the  heated 
tube  into  the  receiver.    It  is  extremely  hygroscopic 
and  its  aqueous  solution  hydrolyzes  so  readily  that 
it   can  be  preserved  only  by  the   addition   of  an 
excess  of  hydrochloric  acid.     On  evaporation  the 
hydroxid  is  the  only  non-volatile  product,  as  the 
hydrochloric  acid  continually  escapes  so  that  more 
of  the  chlorid  is  dissociated  in  order  to  maintain 
the  equilibrium. 

ALUMINUM  CARBONATE  AND  SULFATE.  When  solu- 
tions of  aluminum  salts  are  mixed  with  a  solution  of  a 
carbonate  or  a  sulfid,  aluminum  carbonate  or  sulfid  is 
not  formed  ;  the  products  are  aluminum  hydroxid  and 
carbon  dioxid  or  hydrogen  sulfid.  The  reason  for  this 
is  that  the  salts  of  aluminum  with  weak  acids  cannot 
exist  in  the  presence  of  water.  The  hydrolytic  action 
of  the  water  is  such  as  to  dissociate  the  aluminum  car- 
bonate or  sulfid  into  aluminum  hydroxid  and  carbonic 
acid  or  hydrogen  sulfid.  These  two  substances,  being 
volatile,  escape  from  the  solution.  The  equilibrium  is 
thus  destroyed  so  that  more  of  the  carbonate  or  sulfid  is 
dissociated  ;  the  outcome  is  the  complete  decomposition 
into  aluminum  hydroxid  and  carbon  dioxid  or  hydro- 
gen sulfid. 

377.  Aluminum  Silicates.     Aluminum  silicates 
form  a  large  part  of  the  earth's  crust,  and  in  combi- 
nation with  other  silicates  occur  as  important  min- 
erals.    Feldspar  is  the  most  abundant,  and  together 
with  quartz  and  mica  forms  granite  rock,    Under  the 


284  Elementary  Chemistry 

action  of  the  weather,  .the  feldspar  slowly  disinte- 
grates ;  the  chief  products  are  potassium  and  alum- 
inum silicates.  The  former,  being  soluble,  is  washed 
away,  while  the  latter  is  carried  by  the  action  of 
water  to  places  where  the  current  of  water  slackens 
its  speed,  to  be  deposited  as  beds  of  clay.  Clay  then 
is  aluminum  silicate,  and  is  usually  mixed  with 
various  substances,  such  as  calcium  and  magnesium 
carbonates,  sand,  and  the  oxids  of  iron.  The  better 
kinds  are  employed  in  making  stoneware  and  fire 
brick;  the  colored  varieties  are  used  in  making 
earthenware  and  ordinary  brick. 

Kaolin  is  the  purest  form  of  clay,  and  ;s  hydrated 
aluminum  orthosilicate.  It  has  a  very  high  melting 
point  when  pure,  but  if  mixed  with  feldspar  its 
point  of  fusion  is  lowered  sufficiently  to  make  it  of 
use  in  the  manufacture  of  porcelain. 

378.  Porcelain.     Kaolin  is  mixed  with  limestone 
and  sand  in  such  proportions   as  to   prevent   the 
shrinkage  of  the  clay  when  heated ;  the  ingredients 
are  ground  fine  and  thoroughly  mixed.      Enough 
water  is  added  to  make  the  mixture  plastic.     The 
mass  is  then  given  the  desired  shapes,  carefully 
dried,  and  baked  at  a  high  temperature  in  a  furnace. 
A  glaze  is  put  on  the  product  by  dipping  the  articles 
in  a  mixture  of  powdered  feldspar  and  quartz  sus- 
pended in  water  and  again  heating  or  "  firing  "  them. 
The  adhering  powder  is  thus  made  to  melt  and  form 
a  smooth,  impervious,  and  lustrous  coating. 

379.  Stoneware,     Earthenware,     and    Bricks. 
Stoneware  is  a  coarse  porcelain,  and  crockery  is 
the  best  grade  of  stoneware.     The  materials  for 
stoneware  are  not  so  carefully  selected  as  is  the 


Aluminum  285 

case  with  porcelain,  and  are  not  heated  to  so  high  a 
temperature.  Earthenware  is  made  from  ordinary 
clay.  The  glaze  is  put  on  in  various  ways.  Thus,  it 
may  be  applied  to  the  earthenware  before  " firing," 
or  the  ware  may  be  heated  without  a  glaze  and, 
towards  the  end  of  the  operation,  salt  introduced 
into  the  furnace.  This  volatilizes,  comes  in  con- 
tact with  the  ware,  and  reacts  with  it  to  produce  a 
silicate  of  sodium  and  aluminum  which  melts  and 
forms  a  glaze. 

Bricks  consist  of  unglazed  earthenware,  although 
for  ornamental  purposes  a  glaze  may  be  put  on  one 
or  two  sides.  Their  color  is  mainly  due  to  the 
presence  of  iron  compounds  in  the  clay. 

Exercises  and  Problems 

/.     What  is  the  formula  of  ferric  ammonium  alum  ? 

2.  Terreil,  in  1879,  found  that  0.0455^-  of  hydrogen  were 
evolved  when  0.410  <?"•  of  aluminum  were  dissolved  in  an  acid. 
What  is  the  atomic  weight  of  aluminum  as  calculated  from  this 
experiment  ? 

j.  Mallet,  in  1880,  burned  the  hydrogen  evolved  by  dissolving 
10.3691^-  of  aluminum  in  caustic  soda,  by  passing  the  gas  over 
heated  copper  oxid,  and  obtained  10.351 5  <£"•  of  water.  Calculate 
the  atomic  weight  of  aluminum. 


CHAPTER  XXVII 

TIN    AND    LEAD 

TIN 

380.  Occurrence.     Tin  does  not   occur  native, 
and  is  almost  invariably  found  in  combination  with 
oxygen,  forming  tin-stone  or  cassiteritc,  SnO2.     This 
mineral  is  not  widely  distributed ;  most  of  it  comes 
from   a  group   of  islands  lying  east   of   Sumatra 
(Banca,  Billiton,  and  Sinkop). 

HISTORICAL  NOTE.  It  is  known  that  the  tin  mines 
of  Cornwall  were  worked  long  before  the  Christian  era, 
and  the  metal,  both  pure  and  in  its  alloy  (bronze),  was 
extensively  used  by  the  ancients. 

381.  Metallurgy.      The    tin-stone    is    crushed, 
washed  free  from  earthy  impurities,  and  roasted  in 
a  reverberatory   furnace   to   drive   off   sulfur  and 
arsenic.     It  is  again  washed  and  then  mixed  with 
powdered  anthracite  and  smelted : 

SnO2  +  2C->Sn  +  2  CO 

The  metal  is  purified  by  liquation,  i.  e.,  it  is  gradu- 
ally heated  in  a  furnace  with  an  inclined  floor,  so 
that  the  tin,  which  melts  first,  may  flow  off  from 
the  other  metals  which  may  be  mixed  with  it  and 
which  melt  at  a  higher  temperature. 

382.  Properties.     Physical.     (Table    I.,   Appen- 
dix D.)     Tin  is  a  lustrous,  white  metal,  remaining 
bright  even  in  moist  air.    At  ordinary  temperatures 
it  may  be  readily  beaten  out  into  thin  sheets,  tinfoil, 

[286] 


Tin  and  Lead  287 

and  may  be  drawn  out  into  wire.  At  temperatures 
near  its  melting  point,  however,  it  becomes  brittle 
enough  to  be  easily  powdered. 

Chemical.  When  strongly  heated  in  the  air,  tin 
burns  with  a  brilliant  light  to  stannic  oxid,  SnO2. 
Concentrated  hydrochloric  acid  dissolves  it  slowly, 
forming  hydrogen  and  stannous  chlorid,  SnCl2.  It 
reduces  hot  concentrated  sulfuric  acid  with  forma- 
tion of  stannous  sulfate  and  sulfur  dioxid : 

Sn  +  2  H2S04  ->  SnS04  +  SO2  +  2  H2O 
Nitric  acid   converts   it   into   the   insoluble   meta- 
stannic  acid. 

383.  Uses  and  Alloys.     Tin  is  extensively  used 
in  "tinning"  other  metals,  especially  iron,  by  dip- 
ping them  into  a  bath  of  the  molten  metal.     Tin- 
ware utensils  consist  of  sheet  iron  covered  with  a 
thin  coating  of  tin.     The  copper  of  cooking  dishes 
is  often  tinned,  and  tin-coated  brass  wire  is  made 
into  pins.     Many  useful  alloys  contain  tin.     Pewter 
is  three  parts  tin  to  one  part  lead,  while  solder  con- 
tains equal  parts  of  both  metals.     Bronze  is  a  mix- 
ture of  tin  and  copper.     Tin  amalgam  is  employed 
in  putting  the  reflecting  surface  on  mirrors. 

PRINCIPAL  COMPOUNDS  OF  TIN 

Tin  forms  two  series  of  salts,  stannous,  in  which 
the  metal  is  bivalent;  and  stannic,  in  which  it  is 
quadrivalent. 

384.  Oxids  of  Tin.     Stannous  oxid,  SnO,  a  dark 
brown  powder,  is  unimportant.     Stannic  oxid,  SnO2, 
is  the  principal  ore  of  tin,  and  may  be  prepared  as  a 
white  powder  by  burning  tin  in  the  air  or  by  treat- 
ing the  metal  with  strong  nitric  acid,  evaporating  to 


288  Elementary  CJicmistry 

dryness  and  heating  the  product.  When  fused  with 
caustic  soda,  a  soluble  salt,  sodium  stannatc,  Na2SnO3, 
is  produced,  which  is  used  as  a  mordant  in  the  dye- 
ing of  calico. 

385.  Chlorids  of  Tin.     Stannous  chlorid,  SnCl2,  is 
prepared  by  dissolving  tin  in  hydrochloric  acid.    By 
evaporation  of  the  solution,  a  white,  crystalline  com- 
pound, SnCl2  +  2  H2O,  separates  out,  which  is  called 
tin  salt,  and  is  used  as  a  mordant  in  dyeing.     Stannic 
chlorid,  SnCl4,  is  a  colorless,  fuming  liquid,  prepared 
by  the  action  of  chlorin  on  tin  or  stannous  chlorid. 

386.  Tin  Sulfids.     Tin  foil  takes  fire  in  the  vapor 
of  sulfur,  giving  a  lead-colored   mass  of   stannous 
sulfid,  SnS.     When  hydrogen  sulfid  is  passed  into  a 
solution  of  stannous  chlorid,  the  same  compound 
is  precipitated  as  a  brown  powder.      Stannic  sulfid, 
Sn2S3,  is  prepared  by  heating  tin  amalgam,  sulfur, 
and  ammonium  chlorid  together,  when  it  is  obtained 
as  a  mass  of  golden  yellow  scales.     It  is  used  as  a 
pigment  under  the  name  of  mosaic  gold,  and  is  an 
ingredient  of  bronze  powder.     Stannic  sulfid  is  also 
obtained  as  a  yellow,  amorphous  precipitate  when 
hydrogen  sulfid  is  passed  into  an  acidified  solution 
of  a  stannic  salt. 

LEAD 

387.  Occurrence.     Lead  is  found  native  only  in 
small  quantities,  but  is  found  in  many  parts  of  the 
world  combined  with  sulfur  to  form  galenitc,  PbS. 
Other  minerals  are  the  carbonate,  PbCO3  (ccrussite], 
and  the  sulfate,  PbSO4  (angle site). 

HISTORICAL  NOTE.  Lead  is  one  of  the  seven  metals 
known  to  the  ancients.  It  was  often  called  Saturn, 
from  being  associated  with  the  planet  of  that  name. 


Tin  and  Lead  289 

388.  Metallurgy.     I.     Precipitation  Process.     The 
galenite  is  heated  with  iron,  which  removes  the 
sulfur : 

PbS  +  Fe  -»  FeS  +  Pb 

II.  Reduction  Process.  Galenite  is  heated  in  a 
reverberatory  furnace  with  free  access  of  air.  The 
sulfid  is  thus  partially  oxidized: 

4PbS  +  ;02  ->2PbO  +  2PbS04  +  2S02 

The  supply  of  air  is  then  shut  off  and  the  tempera- 
ture raised,  when  the  unchanged  lead  sulfid  reacts 
with  the  oxid-and  sulfate : 

2  pbO  +  PbS  — >  3  Pb  +  SO2 
PbS04  +  PbS  ->  2  Pb  +  2  S02 

389.  Properties.     Physical.     (Table   I.,   Appen- 
dix D.)     Lead  is  a  soft,  bluish-white  metal  which 
cannot  be  hammered  out  into  foil  or  drawn  into 
wire,  but  is  obtained  in  these  forms  by  rolling  and 
pressing.    A  freshly-cut  surface  is  highly  lustrous, 
but  on  exposure  to  the  air  soon  becomes  tarnished. 
When  a  solution  of  a  lead  salt  is  electrolyzed  or  has 
a  piece  of  zinc  suspended  in  it,  the  metal  separates 
in  the  form  of  beautiful,  lustrous  crystals. 

Chemical.  Lead  dissolves  readily  in  dilute  nitric 
acid,  but  sulfuric  and  hydrochloric  acids  are  almost 
without  action  upon  it.  It  is  unaffected  by  pure 
water  in  the  absence  of  air,  but  in  contact  with  air 
lead  hydroxid  is  formed,  which  is  slightly  soluble 
in  water.  If  the  water  is  hot  or  contains  carbon 
dioxid  or  ammoniacal  salts,  lead  is  dissolved  much 
more  abundantly.  As  lead  salts  are  poisonous, 
drinking  water  which  contains  even  traces  of  such 
substances,  and  which  is  conveyed  in  lead  pipes, 


290  Elementary  Chemistry 

should  not  be  used  until  it  has  run  for  some  time 
so  as  to  cover  the  metal  with  a  coating  of  the 
insoluble  hydroxid  and  carbonate. 

390.  Uses  and  Alloys.    Because  of  the  ease  with 
which  lead  can  be  worked  and  its  power  of  resist- 
ing acids,  it  is  used  in  lining  sulfurie  acid  chambers 
and  some  of  the  cells  used  in  electrolytic  processes. 
As  in  contact  with  water  it  soon  becomes  coated 
with  an  impervious  and  insoluble  layer  of  hydroxid 
and  carbonate,  it  is  also  extensively  used  in  making 
water  pipes.    These  are  made  by  squeezing  hot  lead 
under  great  pressure  through  ring-shaped  apertures 
of  steel.     Ordinary  shot  is  an  alloy  of  lead  with  a 
little  arsenic.     Type  metal  and  solder  are  also  lead 
alloys. 

SOME  IMPORTANT  COMPOUNDS  OF  LEAD 

Lead,  like  tin,  forms  two  series  of  salts ;  the  biva- 
lent series  is  distinguished  as  plumbous  (this  word  is 
but  seldom  used),  and  the  quadrivalent  series  is 
known  &s  plumbic. 

391.  Oxids  of  Lead.      Five  oxids   of   lead  are 
known:       Lead  suboxid  or  plumbous  oxid,  Pb2O, 
plumbic   oxid   (lead   monoxid,   massicot,  litharge), 
BbO,  lead  sesquioxid,  Pb2O3,  triplumbic  tetroxid 
(red  lead,  minium),   Pb3O4,  and   plumbic  peroxid 
(lead  dioxid),  PbO2. 

Plumbic  oxid  is  obtained  when  lead  is  heated  with 
free  access  of  air,  or  when  lead  nitrate  or  carbonate 
or  any  of  the  other  oxids  are  strongly  heated.  It 
forms  a  yellow  powder  commercially  known  as 
massicot,  which  when  melted  and  again  solidified 
yields  a  crystalline  mass  known  as  litliargc.  It  is 


Tin  and  Lead  291 

used  in  the  manufacture  of  some  varnishes  and  oils, 
other  lead  compounds,  flint  glass,  and  as  a  glaze  for 
earthenware. 

Red  lead  is  formed  when  lead  carbonate  or  mon- 
oxid  is  heated  to  above  400°.  It  is  a  red  powder 
used  as  a  common  red  paint  and  in  making  certain 
cements  and  varnishes  as  well  as  flint  glass. 

Lead  dioxid  is  prepared  by  the  action  of  dilute 
nitric  acid  on  red  lead.  It  is  a  brown  powder,  giv- 
ing up  its  oxygen  readily,  so  that  it  is  a  powerful 
oxidizing  agent.  It  is  used  in  storage  batteries. 

392.  Chlorids  of  Lead.     Lead  chlorid,  PbCl7,  is 
obtained   as   a  white    precipitate   when   a   soluble 
metallic  chlorid  is  added  to  a  solution  of  a  lead  salt ; 
also  by  the  action  of  boiling  hydrochloric  acid  on 
lead.     It  is  somewhat  soluble  in  cold  water,  and 
freely  so  in  hot  water.     Lead  tetrachlorid  is  obtained 
as  a  yellow,  unstable  liquid  when  lead  dioxid  is  dis- 
solved in  strong,  cold  hydrochloric  acid. 

393.  Lead    Sulfate,    PbSO4.      Lead  sulfate  is 
formed  when  a  soluble  sulfate  is  added  to  a  solution 
of  some  lead  salt.      It  is  a  white,  insoluble  powder, 
sometimes  used  as  an  adulterant  of  white-lead  paint. 

394.  Lead  Nitrate,  Pb(NO3)2.     Lead  nitrate  is 
obtained  by  dissolving  lead  or  litharge  in  dilute 
nitric  acid.      It  forms  white  crystals  freely  soluble 
in  water.     When  heated  it  decomposes  into  litharge, 
nitrogen  peroxid,  and  oxygen. 

395.  Lead  Sulfid,  PbS.     Lead  sulfid  occurs  nat- 
urally as  galenite  and  may  be  obtained  as  a  black 
precipitate  by  passing  hydrogen  sulfid  into  a  solu- 
tion of  a  lead  salt.     When  heated  in  the  air  it  is 
oxidized  to  lead  sulfate. 


292  Elementary  Chemistry 

396.  Lead    Carbonates.     (White  Lead.)     When 
ammonium  carbonate  solution  is  added  to  a  solution 
of  lead  nitrate  or  acetate,  a  white,  crystalline  powder 
is  precipitated,  which   is  lead   carbonate,   PbCO3. 
Sodium  or  potassium  carbonate  precipitates  from 
lead  solutions  basic  carbonates,  varying  somewhat 
in  composition.     The  most  important  of  these  is 
white  lead.     This  compound  is  a  valuable  ingredient 
of  paint  and  is  manufactured  by  several  processes ; 
the  best  and  longest  known  is  the  Dutch  method. 

DUTCH  METHOD.  The  lead  is  cast  into  gratings 
called  "  buckles,"  which  are  placed  in  earthenware  pots. 
A  little  vinegar  or  dilute  acetic  acid  is  added  and  the 
pots  are  placed  on  a  thick  layer  of  spent  tanbark  upon 
the  floor  of  a  shed.  The  pots  are  covered  over  with 
planks,  upon  which  is  placed  more  tanbark  and  a  sec- 
ond tier  of  pots.  This  is  continued  up  to  the  roof  of 
the  shed.  The  tanbark  ferments  and  thereby  becomes 
heated  so  that  the  acid  is  gradually  vaporized  and 
attacks  the  lead,  and  the  carbon  dioxid  which  is  lib- 
erated also  attacks  the  metal.  The  reactions  are  com- 
plicated and  not  well  understood.  In  three  or  four 
months  the  process  is  complete.  The  contents  of  the 
jars  are  then  sifted  so  as  to  separate  the  white  lead 
from  the  unattacked  lead  and  the  product  ground  with 
water  and  dried.  The  value  of  white  lead  is  due  to  its 
"body"  or  covering  power.  It  is  very  poisonous  and 
turns  black  in  air  containing  hydrogen  sulfid. 

OTHER  METHODS.  In  the  German  process  sheets  of 
lead  are  hung  up  and  a  mixture  of  steam,  carbon  dioxid, 
and  the  vapor  of  acetic  acid  blown  over  them.  In  the 
French  process  carbon  dioxid  is  passed  into  a  solution 
containing  lead  acetate  and  oxid. 

397.  Lead  Acetate,  Pb(C  2  H  3  O  2 )  2 .    Lead  acetate 
is  formed  by  dissolving  lead  in  dilute  acetic  acid. 
It  is  a  white,  crystalline  salt  with  a  sweetish  taste, 
and  is  commonly  called  "  sugar  of  lead/' 


Tin  and  Lead  293 

Exercises 

/.  Why  is  white-lead  paint  not  suitable  for  covering  the  walls 
of  a  chemical  laboratory  ? 

2.  What  three  insoluble  chlorids  have  thus  far  been  studied  ? 
In  what  liquids  are  they  soluble  ? 

3.  What  valency  has  each  of  the  metals  in  each  of  the  follow- 
ing compounds:    ZnBr2  ;   SbH3  ;   AuCl3  ;   CdO  ;   SnCl4;   AUO3  ; 
BaCO3  ;  LiCO3  ;  KNO3? 

Problems 

1.  (a)    Van  der  Plaats,  in  1885,  found  that  45. 8323 <£"•  of  tin, 
when  oxidized,  gave  58.2519^".  of  SnO2.     If  the  atomic  weight  of 
oxygen  is  16.00,  what  is  that  of  tin  ? 

(I)}  The  same  investigator  also  found  that  on  reducing 
17.2935  £•  of  SnO.,  with  hydrogen,  I3.6O56.?"-  of  metal  were  obtained. 
What  is  the  atomic  wreight  of  tin  ? 

2.  Dumas  found  that  the  chlorin  in  4. 504^-  of  tin  chlorid  was 
equivalent  to  7.481^"-  of  silver.      If  the  atomic  weights  of  silver 
and  chlorin  are  107.94  an^  35-45,  respectively,  what  is  the  atomic 
weight  of  tin  ? 

j.  Dumas,  in  1859,  obtained  from  28. 409^-  of  tin  36.121  &•  of 
its  oxid.  What  is  the  atomic  weight  of  tin  ? 

4.  Dumas,  in  1859,  added  to  a  solution  containing  4.504.^.  of 
stannous  chlorid  an  excess  of  a  solution  of  silver  nitrate  and  found 
that  the  precipitate  of  silver  chlorid  formed  contained  7.481  g-  of 
silver.     What  is  the  atomic  weight  of  tin,  it  being  assumed  that 
the  atomic  weights  of  chlorin  and  of  silver  are  35.43  and  107.94, 
respectively  ? 

j.  How  many  pounds  of  lead  and  of  sulfur  are  contained  in 
800  pounds  of  galenite,  PbS  ? 


CHAPTER  XXVIII 


COPPER,   SILVER,    GOLD,   AND   PLATINUM 

COPPER 

398.  Occurrence.     Copper  occurs  native  in  sev- 
eral places,  notably  in  the  Lake  Superior  region. 
Its  principal  minerals  are  chalcocite,  Cu2S,  chalcopy- 
rite,  CuFeS2,  malachite,  CuCO3,  Cu(OH)2,  and  ruby 

^copper  or  cuprite,  Cu2O. 

HISTORICAL  NOTE.  Copper  has  been  known  from 
the  earliest  times.  Alloyed  with  tin,  it  forms  bronze, 
which  was  used  to  make  weapons,  before  the  art  of 
extracting  iron  from  its  ores  was  invented. 

399.  Metallurgy.     I.    Dry  Way.    The  sulfid  ores 
are  partially  converted  into  oxids  by  roasting,  and 
then  strongly  heated,  when  the  following  reaction 
ensues : 

Cu2S  +  2Cu2O  -»  6Cu  +  SO2 

II.  Wet  Way.  The  ores  are  converted  into  the 
soluble  chlorid  by  heating  with  common  salt,  or 
into  the  soluble  sulfate  by  treatment  with  a  solution 
of  iron  sulfate.  The  copper  is  then  thrown  out  of 
solution  by  metallic  iron  or  by  electrolysis. 

PURIFICATION  OF  COPPER.  The  crude  copper  thus 
obtained  is  usually  purified  by  electrolysis.  The  copper 
is  cast  into  thick  plates  which  are  suspended  in  a  solu- 
tion of  acidified  copper  sulfate.  Thin  sheets  of  pure 
copper  are  also  hung  in  the  solution.  The  crude  copper 
sheets  are  made  the  anodes,  and  pure  copper  sheets 
the  cathode  of  a  powerful  electric  current.  Pure  cop- 
per is  deposited  from  the  solution  on  the  cathode  and 

[294] 


Copper,  Silver,  Gold,  and  Platinum  295 

an  equivalent  amount  of  copper  dissolved  from  the 
anode.  The  concentration  of  the  solution  thus  remains 
unchanged,  while  the  copper  passes  from  anode  to 
cathode.  The  impurities  of  the  crude  copper  fall  down 
beneath  the  anode,  forming  the  so-called  "anode-mud," 
from  which  gold  and  silver  are  obtained  in  paying  quan- 
tities. This  " electrolytic  copper"  is  very.  pure. 

400.  Properties.     Physical.     (Table  I.,  Appendix 
D.)     Copper  is  a  reddish  metal  with  considerable 
ductility  and  tenacity,  and  is  an  excellent  conductor 
of  heat  and  electricity. 

Chemical.  Copper  is  unaffected  by  dry  air  except 
when  heated  to  nearly  a  red  heat,  when  it  combines, 
with  oxygen  to  form  the  black  oxid  of  copper,  CuO. 
In  moist  air  it  slowly  becomes  covered  with  a  green 
coating,  verdigris,  which  is  a  hydrated  copper  carbo- 
nate. It  burns  in  chlorin,  but  is  only  slowly  acted 
upon  by  hydrochloric  acid.  Nitric  acid  dissolves 
it  with  formation  of  nitrogen  oxids  and  copper 
nitrate,  Cu(NO3)2 ;  sulfuric  acid  does  the  same, 
producing  the  sulfate,  CuSO4,  and  sulfur  dioxid. 
Vegetable  acids,  fats,  and  common  salt  act  upon 
copper  when  exposed  to  the  air,  and  since  copper 
salts  are  poisonous,  eatables  containing  vinegar  or 
salt  should  not  be  preserved  in  copper  utensils. 

401.  Uses  and  Alloys.     Copper  is  used  exten- 
sively in  many  ways,  such  as  in  conductors  for  elec- 
tric currents,  in  making  coins  and  stills,  in  covering 
roofs  and  ships'  bottoms.     Some  kinds  of  engrav- 
ings, maps,  and  etchings  are  prepared  on  copper 
plates,  and  books  are  printed  and  illustrated  from 
an  electrotype  prepared  by  depositing  a  thin  coating 
of  copper  in  a  mold  of  the  type  or  design.     Copper 
also  enters  into  the  composition  of  a  number  of 


296  Elementary  CJicmistry 

valuable  alloys.  Brass  is  a  mixture  of  copper  and 
zinc  in  proportions  varying  according  to  the  kind  of 
brass  desired.  Gun  metal  and  bell  metal  are  alloys 
of  tin  and  copper.  German  silver  is  an  alloy  of 
copper,  zinc,  and  nickel. 

SOME  IMPORTANT  COMPOUNDS  OF  COPPER 

Copper  forms  two  series  of  compounds,  in  one  of 
which  (cuprous)  it  is  univalent,  and  in  the  other 
(cupric),  bivalent. 

402.  Copper  Oxids.     Cuprous   oxid,   Cu2O,    is   a 
red  substance  insoluble  in  water. 

Cupric  oxid,  CuO,  is  made  by  heating  copper  to 
redness  with    free    access    of    air,  and   by  heating 
copper  nitrate  or  carbonate  or  hydroxid;  the  last- 
named  compound  is   formed  when   a  fixed  alkali 
solution  is  added  to  a  solution  of  a  copper  salt : 
CuSO4  +  2KOH  -^  Cu(OH)2  +  K2SO4 
Cu(OH)2  ->CuO  +  H20 

403.  Copper  Sulfate,  CuSO4  +  5  H2O.     Copper 
sulfate  is  made  by  the  action  of  hot  concentrated 
sulfuric  acid  on  copper,  and  is  also  obtained  as  a 
by-product  in  the  refining  of  gold  and  silver.     It  is 
commercially  known  as  "blue  vitriol,"  and  is  used 
extensively  in  copper-plating,  in  galvanic  batteries, 
and  in  making  paint.     Its  five  molecules  of  Avater  of 
crystallization  can  be  expelled  by  heating,  leaving  a 
grayish  residue  of  anhydrous  copper  sulfate,  which 
turns  blue  when  brought  in  contact  with  water. 

404.  Copper  Nitrate,  Cu(NO3)2.     When  nitric 
acid  acts  on  copper,  the  acid  is  reduced  and  a  very 
soluble,  blue   salt   is   produced.     When  heated,  it 
decomposes  into  cupdc  oxid  and  oxids  of  nitrogen. 


Copper,  Silver,  Gold,  and  Platinum  297 

405.  Copper   Sulfid,    CuS.       Copper    sulfid    is 
formed  as  a  black  precipitate  when  hydrogen  sulfid 
or  an  alkalin  sulfid  is  added  to  a  solution  of  a  cop- 
per salt. 

COPPER-PLATING.  Copper-plating  consists  in  depos- 
iting upon  an  object  a  coating  of  copper.  An  iron  wire 
placed  in  a  copper  sulfate  solution  in  a  short  time 
becomes  covered  with  a  coating  of  copper.  Usually, 
however,  the  plating  is  effected  by  means  of  electrolysis, 
and  the  process  is  extensively  used  in  electrotyping,  or 
the  reproduction  of  type  and  cuts.  A  plaster  of  Paris 
or  wax  mold  is  made  of  the  type,  and  dusted  over  with 
finely  powdered  graphite  so  as  to  make  it  conduct  elec- 
tricity. This  is  placed  in  a  solution  of  copper  and  made 
the  cathode  of  an  electric  current,  of  which  the  anode 
is  a  copper  plate.  When  the  current  passes,  copper  is 
deposited  on  the  mold  and  a  perfect  reproduction  of 
the  type  is  obtained  as  a  thin  coat  of  copper.  This  is 
removed  from  the  mold  and  type  metal  poured  into  it 
so  as  to  give  the  electrotype  the  required  strength  and 
firmness. 

SILVER 

406.  Occurrence.      Silver  occurs  native,  some- 
times in  large   masses,  but  usually  in   crystalline 
threads  and  scales  in  the  fissures  of  rocks.     Besides 
in  horn  silver,  AgCl,  it  occurs  in  combination  with 
sulfur,  as  argent  it  e,  Ag2S,  and  pyrargyritc,  Ag3SbS3. 
The  principal  silver  mines  are  in  Mexico,  South 
America,  Colorado,  Nevada,  Australia,  and  India, 
although  a  good  deal  of  silver  is  obtained  from  lead 
ores,  with  which  it  is  mixed  in  small  proportions. 

HISTORICAL  NOTE.  Silver  was  one  of  the  seven 
metals  of  the  ancients.  It  was  called  hina  by  the  old 
chemists  because  its  color  was  fancied  to  resemble  that 
of  the  moon  (the  Latin  word  for  moon  is  lima).  This 
name  is  perpetuated  in  the  common  name  for  silver 
nitrate,  lunar  caustic. 


298  Elementary  Chemistry 

407.  Metallurgy.    I.   Amalgamation  Process.   The 
ore  is  crushed,  mixed  with  common  salt  and  roasted. 
The  silver  chlorid  thus   formed  is  shaken  up  in 
revolving  cylinders  with  scrap  iron,  mercury,  and 
water,     The  iron  takes  the  chlorin  from  the  silver, 
which  then  forms  an  amalgam  with  the  mercury. 
The  mercury  is  separated  from  the  silver  by  distil- 
lation. 

1 1 .  Zinc  or  Parkes"  Process.  Silver  is  also  separated 
from  lead  by  means  of  zinc,  which  is  but  very  slightly 
soluble  in  lead.  The  lead  containing  silver  is 
melted  in  large  tanks  and  slabs  of  zinc  thrown  in. 
These  float  about  and  gather  together  all  of  the 
silver.  The  alloy  thus  formed  is  removed  and  dis- 
tilled ;  the  zinc  passes  off  and  leaves  the  silver. 

CUPELLATION.  When  lead  contains  a  considerable 
proportion  of  silver,  this  may  be  extracted  by  heating 
the  alloy  in  a  cupel,  a  shallow  dish  made  of  bone  ash. 
The  lead  oxidizes  and  the  lead  oxid  melts  and  is  absorbed 
by  the  porous  bone-ash  cupel,  leaving  the  silver.  This 
process  is  especially  used  in  the  analysis  technically 
called  assay  of  silver  ores. 

408.  Properties.     Physical.      (Table    I.,   Appen- 
dix D.)     Silver  is  the  whitest  of  the  metals  and  has 
a  very  high  luster;  its  polished  surface  is  one  of 
the  best  reflectors  of  light.     It  is  very  malleable 
and  ductile,  and  is  the  best  known  conductor  of 
heat  and  electricity. 

Chemical.  Silver  does  not  oxidize  in  the  air  at 
any  temperature  under  ordinary  pressures,  though 
molten  silver  dissolves  oxygen,  which  is  given  off 
when  it  solidifies.  The  tarnishing  of  silverware  is 
due  to  the  action  of  hydrogen  sulfid  which  is  often 
present  in  minute  proportions  in  the  atmosphere. 


Copper,  Silver,  Gold,  and  Platinum  299 

"  Oxidized  "  silver  is  really  "  sulfidized  "  silver ;  it 
is  formed  by  the  action  of  a  soluble  sulfid  on  silver. 
Dilute  nitric  acid  and  hot  sulfuric  acid  convert  sil- 
ver into  the  nitrate,  AgNO3,  and  sulfate,  Ag2SO4, 
respectively ;  the  acids  themselves  are  reduced  and 
do  not  give  up  hydrogen.  Silver  is  not  dissolved 
by  hydrochloric  acid,  as  its  chlorid  is  insoluble. 

409.  Uses  and  Alloys.    The  main  applications 
of  silver  are  in   coinage,  jewelry,  and  tableware. 
Pure  silver  is  too  soft  for  these  purposes  and  hence 
it  is  alloyed  with  copper,  which  makes  it  harder  and 
more  durable.     Each  country  fixes  by  law  the  ratio 
of  silver  to  copper  in  its  coinage ;  usually  it  is  90 
to  10.     " Sterling  silver"  also  contains  about  these 
proportions. 

SILVER-PLATING.  Silver-plating  was  at  first  done  by 
covering  some  metal  or  alloy  with  a  thin  plate  of  silver, 
which  was  made  to  adhere  by  passing  the  sheets 
between  rollers.  The  plating  was  also  done  by  cover- 
ing the  object  with  silver  amalgam  and  then  driving  off 
the  mercury  by  heat,  as  well  as  by  rubbing  the  article 
with  a  mixture  of  silver  chlorid,  common  salt,  chalk,  and 
potash.  Nowadays  it  is  almost  universally  done  by 
electrolysis.  The  article  is  attached  to  the  cathode  of 
an  electric  circuit  and  suspended  in  a  solution  of  silver 
cyanid,  AgCN,  containing  potassium  cyanid,  KCN, 
while  a  plate  of  silver  forms  the  anode.  "  Frosted  silver  " 
is  obtained  by  dipping  the  hot  metal  into  sulfuric  acid 
for  a  few  moments. 

Mirrors  are  silvered  by  placing  them  in  a  bath  con- 
taining some  silver  compound  and  a  reducing  agent. 

SOME    IMPORTANT   COMPOUNDS   OF   SILVER 

410.  Properties.     Silver    is    always    univalent. 
Its   compounds    are   usually   white,    and   many   of 
them    undergo    decomposition    when    exposed    to 


3OO  Elementary  Chemistry 

light.     The  Latin  name  of  silver,  argentum,  is  often 
used  in  naming  its  compounds,  as  argentic  nitrate. 

SILVER  OXID,  Ag2O.  Silver  oxid  may  be  prepared 
by  mixing  strong  solutions  of  silver  nitrate  and  potas- 
sium hydroxid.  The  hydroxid  at  first  precipitated  soon 
loses  water  and  becomes  changed  into  the  oxid.  Silver 
oxid  is  a  dark  brown,  heavy  powder,  slightly  soluble  in 
water ;  the  solution  is  feebly  alkalin.  When  heated  it 
breaks  up  into  silver  and  oxygen  (§  30).  A  solution 
of  the  oxid  in  ammonium  hydroxid  deposits  crystals 
of  an  explosive  compound  known  as  "  fulminating  silver." 

411.  Silver  Nitrate,  AgNO3.     Silver  nitrate  is 
made  by  dissolving  silver  in  hot  and  dilute  nitric 
acid.     By  evaporating  the  solution,  colorless  crys- 
tals are  obtained.     These,  when  melted  and  cast 
into  sticks,  form  "  lunar  caustic,"  used  by  surgeons 
to   cauterize   flesh.      Silver   nitrate   in   solution   is 
decomposed  by  organic  compounds,  yielding  silver 
as  a  fine  black  powder.     Indelible  ink  is  a  solution 
of  silver  nitrate  in  water  containing  a  little  gum. 
Hair  dyes  also  frequently  contain  this  salt. 

412.  Silver  Chlorid,  AgCl.    Silver  chlorid  occurs 
in  nature   as   the   mineral,  horn   silver,  so   called 
because    of    its    tough,    horn-like    texture,    and    is 
obtained  as  a  white  precipitate  when  any  solution 
of  a  soluble  chlorid  is  added  to  a  solution  of  a  silver 
salt.     It  is  soluble  in  ammonium  hydroxid  and  in 
solutions  of  the  alkalin  thiosulfates. 

413.  Silver    Bromid,    AgBr,    and    lodid,    Agl. 
Silver  bromid  and  iodid  may  be  prepared  by  adding 
any  soluble  bromid  or  iodid  to  a  silver  nitrate  solu- 
tion.    They  are  both  yellow,  insoluble  compounds. 
They  differ  from  silver  chlorid  in  not  being  very 
soluble  in  ammonium  hydroxid. 


Copper,  Silver,  Gold,  and  Platinum  301 

PHOTOGRAPHY 

ACTION  OF  LIGHT.  Photography  is  based  on  the 
fact  that  light  brings  about  the  decomposition  of  the 
halid  salts  of  silver.  Although  this  fact  was  known 
as  early  as  the  sixteenth  century,  yet  the  art  was  not 
developed  until  nearly  the  middle  of  the  nineteenth 
century,  when  Daguerre  discovered  the  action  of  the 
developer.  The  art  of  photography  as  now  practiced  is 
essentially  as  follows.  It  involves  :  First,  the  prepara- 
tion of  the  negative,  and  second,  the  printing  of  the 
positive. 

THE  NEGATIVE.  Glass  plates  are  covered  with  a 
mixture  or  emulsion  of  gelatin  and  silver  bromid  or 
iodid  ;  the  operation  is  carried  out  in  a  room  but  dimly 
lighted  with  red  light,  which  has  a  very  slow  action  on 
silver  salts.  These  gelatin-bromid  plates  are  packed 
in  light-tight  boxes,  and  are  introduced  into  the  camera, 
of  which  there  are  a  multitude  of  forms  on  the  market, 
with  the  film  side  next  the  lens.  During  the  exposure 
no  picture  appears  on  the  plate.  This  is  first  brought 
out  by  the  developer.  To  develop  the  picture  it  is  placed 
in  a  solution  of  a  developer,  such  as  pyrogallic  acid  with 
sodium  carbonate.  Those  parts  affected  by  the  light 
are  now  made  visible  and  the  picture  appears,  but  with 
the  lights  and  shadows  reversed.  The  next  operation 
is  that  of  fixing  and  consists  in  dissolving  out  the  halid 
salt  which  has  not  been  affected  by  the  light.  A  solu- 
tion of  sodium  thiosulfate  ("hyposulfite")  is  used  for 
this  purpose.  The  negative  is  now  complete  and  shows 
the  picture  with  its  light  parts  dark  and  its  dark  parts 
light. 

THE  POSITIVE.  Paper  is  covered  on  one  side  by  a 
layer  or  film  of  albumen  which  is  sensitized  by  depos- 
iting in  it  silver  chlorid.  This  is  done  by  first  floating 
the  paper  on  sodium  chlorid  solution  and  then  on  silver 
nitrate  solution  ;  silver  chlorid  is  thus  produced  right  in 
the  albumen  by  the  reaction  of  the  two  salts.  The 
sensitized  paper  is  placed  with  its  film  against  that  of 
the  negative  in  a  "  printing  frame  "  and  exposed  to  sun- 
light. "The  picture  thus  printed  is  next  toned  &s&  fixed. 
Toning  consists  in  dipping  the  positive  in  a  solution  of 


302  Elementary  Chemistry. 

gold  or  platinum  chlorid  whereby  the  silver  is  partially 
replaced  by  the  gold.  Fixing  is  done  with  sodium  thio- 
sulfate,  as  in  the  case  of  the  negative. 

GOLD 

HISTORICAL  NOTE.  Gold  has  been  known  since  the 
earliest  times.  Owing  to  the  yellow  color  of  both,  it 
was  supposed  by  the  ancient  chemists  that  there  was 
some  connection  between  it  and  the  sun.  For  many 
centuries  it  was  the  aim  of  chemists,  or  rather  alchem- 
ists, to  convert  substances  into  gold,  the  noblest  of  the 
metals.  They  fancied  that  there  might  be  prepared  a 
substance  which  they  called  the  Philosopher's  Stone, 
that  would  effect  this  transmutation. 

414.  Occurrence.      In  small  quantities  gold  is 
found  native  in  many  localities,  principally,  how- 
ever, in  California  and  some  other  western  states, 
Australia,  Siberia,  South  Africa,  and  Alaska.     It  is 
rarely  found  in  combination.    The  native  gold  occurs 
mainly  in  the  veins  of  quartz  rocks.     As  these  are 
disintegrated  by  the  weather,  the  quartz  sand  and 
gold  are  carried  down  creeks  and  rivers  and  depos- 
ited where  the  current  runs  slowest. 

415.  Metallurgy.     Several  methods  are  in  use. 
Placer  mining  consists  in  washing  earth,  gravel,  and 
sand  that  contain  gold  in  a  rapid  current  of  water, 
which  carries  away  the  lighter  particles. 

In  hydraulic  mining  a  powerful  stream  of  water 
is  thrown  against  a  gravel  bank,  and  the  water  carries 
away  the  disintegrated  material  down  through  long 
wooden  troughs  or  " sluices"  in  which  are  placed 
cross-pieces  of  wood.  These  catch  the  heavier 
particles,  while  the  lighter  ones  are  swept  along. 
The  heavy  particles  obtained  in  both  placer  and 
hydraulic  mining  are  treated  with  mercury,  with 


Copper,  Silver,  Gold,  and  Platinum  303 

which  the  gold  forms  an  amalgam,  and  this  is  sep- 
arated and  distilled,  leaving  the  gold  in  the  retort. 

In  quartz  mining  the  gold-bearing  rock  is  crushed 
to  a  powder  in  "  stamp  mills,"  and  the  gold  separated 
as  in  hydraulic  mining. 

In  the  cyanid  process  the  ore  is  pulverized  and 
treated  with  potassium  cyanid  solution  which  dis- 
solves the  gold.  It  is  thrown  out  of  solution  by 
the  addition  of  iron. 

SEPARATION  OF  GOLD  FROM  SILVER.  Usually  gold 
ores  contain  silver  as  well,  and  the  product  obtained  is 
an  alloy  of  these  metals.  If  gold  does  not  form  more 
than  a  quarter  of  the  alloy,  the  silver  can  be  dissolved 
out  by  boiling  with  sulfuric  acid.  This  process  is 
accordingly  known  as  quart ation.  When  but  little 
silver  is  present,  the  alloy  is  dissolved  in  aqua  regia 
and  the  gold  thrown  out  of  the  diluted  solution  by  the 
addition  of  iron  sulfate. 

The  Electrolytic  Method  is  coming  into  use.  The 
anode  consists  of  an  alloy  of  gold  and  silver.  The 
cathode  is  silver,  and  the  electrolyte  is  nitric  acid. 
When  the  circuit  is  closed,  the  silver  of  the  anode  goes 
into  solution,  leaving  the  gold  as  a  fine  powder,  which  is 
caught  in  a  cloth  bag  which  surrounds  the  whole  anode. 

416.  Properties.     Physical.      (Table    I.,   Appen- 
dix D.)     Gold  is  a  yellow  metal  with  very  brilliant 
luster ;  it  is  the  most  malleable  and  ductile  of  all  the 
metals,  and  is  a  very  good  conductor  of  heat  and 
electricity. 

Chemical.  Gold  is  not  acted  upon  by  any  ele- 
ments excepting  the  halogens,  and  is  soluble  only 
in  aqua  regia. 

417.  Uses  and  Alloys.     Gold  is  extensively  used 
in  jewelry  and  money.     The  pure  metal  is  too  soft 
to  withstand  much  usage ;  hence  it  is  alloyed  with 


304  Elementary  Chemistry 

silver  or  copper  or  both,  according  to  the  shade  of 
color  and  the  degree  of  hardness  desired.  United 
States  coins  contain  900  parts  gold  to  100  of  copper 
and  are  said  to  be  "  900  fine."  Jewelers  express  the 
relative  purity  of  gold  in  carats.  Thus,  24-carat  gold 
is  pure,  i8-carat  gold  contains  \\  gold,  i4-carat,  \\ 
gold,  and  so  on.  Considerable  gold  in  the  form  of 
"gold  leaf"  is  used  as  fillings  for  teeth  and  for  gild- 
ing ornamental  work  on  book  covers,  signs,  furni- 
ture, and  buildings. 

GOLD-PLATING.  Gold-plating  is  usually  done  by 
electrolysis ;  a  solution  of  gold  in  potassium  cyanid  is 
used  as  the  electrolyte. 

418.  Compounds  of  Gold.      Gold   dissolves   in 
aqua  regia  with  formation  of  auric  chlorid,  AuCl3, 
used  in  "toning"  in  photography.     Auric  chlorid, 
when  heated,  loses  chlorin  and  is  converted  into 
aurous  chlorid,  AuCl.     If  stannous  chlorid,  SnCl2, 
solution  be  mixed  with  a  solution  of  auric  chlorid,  a 
purple-colored  precipitate,  known  ®& purple  of  Cassim, 
is  formed. 

PLATINUM 

419.  Properties.     Platinum  is  found  in  the  Ural 
Mountains  either  free  or  alloyed  with  some  of  the 
rare  metals,  iridium,  palladium,  rhodium,  ruthenium, 
and  osmium.      It  is  a  white,  lustrous  metal,  very 
malleable  and  ductile,  and  melts  only  at  the  highest 
temperatures.     Acids  have  no  action  upon  it,  but 
aqua  regia  dissolves  it,  forming  platinum  chlorid, 
PtCl4,  which  is  used  in  "toning"  in  photography. 
Platinum  is  attacked  by  alkalin  hydroxids.      It  is 
used  in  making  stills,  crucibles,  foil,  and  wire  for 
the  laboratory. 


Copper,  Silver,  Gold,  and  Platinum  305 

NOTE.  When  platinum  chlorid  is  heated  to  redness  the  chlorin 
is  driven  off,  leaving  the  platinum  in  a  very  finely  divided  state. 
This  spongy  platinum,  as  well  as  a  finer  form  called  platinum 
black,  has  the  property  of  adsorbing  or  occluding  gases.  Oxygen 
thus  occluded  is  much  more  energetic  than  ordinary  oxygen. 

Exercises 

1.  How  has  cupric  oxid  been  employed  in  verifying  the  Law 
of  Definite  Proportions  by  mass  or  weight  ? 

2.  If  given  an  ore  supposed  to  contain  silver,  how  would  you 
make  a  test  for  the  presence  of  that  metal  ? 

j>.  Write  the  equation  for  the  reaction  between  hot  concen- 
trated sulfuric  acid  and  copper. 

4.  Why  is  it  customary  to  employ  a  wooden  and  not  a  silver 
mustard  spoon  ? 

Problems 

/.  How  many  grams  of  silver  nitrate  would  be  required  to 
make  20^-  of  silver  chlorid  ? 

2.  Hampe,  in  1874,  reduced  2o.6SS5<^  of  copper  oxid  in  hydro- 
gen and  obtained  i6.5i67^  of  copper.  Calculate  the  atomic 
weight  of  copper. 

j>.  How  many  grams  of  silver  nitrate  can  be  prepared  by  dis- 
solving is.?"-  of  silver  in  nitric  acid,  evaporating  to  dryness,  and 
melting  the  residue? 

4.  What  is  the  value  of  the  silver  in  10^-  of  a  10  per  cent 
solution  of  silver  nitrate,  if  one  ounce  of  silver  is  worth  60  cents? 

5.  Stas  burned   IOI.SIQ^-    of  silver  in  a  current  of  chlorin 
and  obtained  134.  S6i<r-  of  silver  chlorid.     What  are  the  combining 
weights  of  silver  and  chlorin  ? 

6.  Richards,  in  1889,  dissolved  4.39313  <?"•  of  copper  in  silver 
nitrate  solution,  whereby  I4.9io4<£"-  of  silver  were  precipitated.    If 
the  atomic  weight  of  silver  is  107.94,  calculate  that  of  copper. 

7.  Shaw,  in  1887,  passed  the  same  electric  current  through 
solutions  of  copper  and  silver  salts  and  found  the  ratio  of  the 
weights  of  the  metals  precipitated  to  be  i  :  3.4000,  respectively. 
Taking  the  atomic  weight  of  silver  as  107.94,  calculate  that  of 
copper. 

8.  From  10  c.c.  of  a  solution  of  silver  nitrate  o.936s<?"-  of  silver 
chlorid  were   obtained  by  precipitation  with   hydrochloric  acid. 
How  many  grams  of  silver  nitrate  are  contained  in  a  liter  of  the 

solution  ? 

21 


CHAPTER  XXIX 


IRON,  NICKEL,  AND  COBALT 

IRON 

420.  Occurrence.     Iron   is   not   only  the   most 
useful  of  the  metals,  but  is  also  one  of  the  most 
abundant  and  most  widely  distributed.    Native  iron 
occurs  but  rarely ;  meteorites  contain  a  large  pro- 
portion of  the  pure  metal. 

The  principal  ores  of  iron  are  magnetite  (lodestone), 
Fe3O4  ;  hematite,  Fe2O3  ;  limonite,  a  hydrated  oxid, 
and  siderite  (spathic  iron  ore),  FeCO3.  Iron  pyrites 
(fool's  gold*),  FeS2,  although  very  abundant,  cannot 
be  used  in  obtaining  the  metal  because  of  the  objec- 
tionable properties  communicated  to  iron  from  even 
a  very  slight  admixture  of  sulfur.  It  is  used  exten- 
sively as  a  source  of  sulfur  in  the  manufacture  of 
sulfuric  acid  (§  278). 

421.  Metallurgy.      The  ores  of  iron  are  oxids, 
hydroxids,  or  carbonates,  and  are  reduced  by  heat- 
ing them  with  carbon  in  the  form  of  charcoal,  coke, 
or  coal.     The  chief  impurity  of  the  ores  is  sand 
(silica).    As  this  can  combine  with  iron  to  form  iron 
silicate,  to  prevent  the  loss  of  the  metal  thus  occa- 
sioned, limestone  (calcium  carbonate)  is  added  to 
the  mixture  of  carbon  and  ore,  whereby  the  silica 
combines  with  the  calcium  instead  of  the  iron.    The 
molten  calcium  silicate,  or  slag,  does  not  mix  with 
melted  iron,  but  floats  upon  it. 

[306] 


Iron,  Nickel,  and  Cobalt 


307 


By  courtesy  of  the  SCIENTIFIC  AMERICAN 
Fig-   37 A  MODERN  BLAST  FURNACE   IN  OPERATION 

The  reduction  is  effected  in  a  blast  furnace 
(Fig.  37).  This  is  a  structure  about  seventy  feet 
high,  made  of  plates  of  iron  bound  together  and 
lined  with  fire  brick.  The  furnace  is  nearly  filled 
from  the  top  with  the  ore,  fuel,  and  limestone;  a 


308  Elementary  Chemistry 

little  of  each  is  added  at  a  time  so  as  to  secure 
a  thorough  mixing  of  the  three  substances.  A 
powerful  blast  of  heated  air  is  blown  in  through 
pipes  called  tuyeres  (pronounced  tiveers)  near  the 
bottom.  As  the  reduction  of  the  metal  proceeds,  it 
collects  as  a  liquid  at  the  bottom  of  the  furnace  with 
the  molten  slag  floating  upon  it.  Every  few  hours 
the  slag  and  the  iron  are  drawn  off;  the  latter  is 
run  out  into  molds  where  it  solidifies  into  bars  called 
"pigs";  the  metal  itself  is  known  as  "pig  iron." 
Charges  of  fuel,  ore,  and  limestone  are  introduced 
into  the  top  of  the  furnace  at  frequent  intervals ;  its 
operation  is  thus  made  continuous  for  months  and 
even  years. 

422.  Chemistry  of  the  Process.     The  chemical 
reactions  involved  in  the  reduction  are  the  following: 
The  carbon  of  the  fuel  in  the  lower  part  of  the  fur- 
nace unites  with  the  oxygen  of  the  air  forced  in  to 
form  carbon  dioxid,  which,  as  it  passes  through  the 
highly  heated  fuel  above  it,  is  reduced  to  the  mon- 
oxid.    The  carbon  monoxid  unites  with  the  oxygen 
in  the  ore,  forming  carbon  dioxid,  while  the  iron  is 
set  free : 

Fe203  +3CO->2Fe  +  3C02 

The  gases  which  pass  from  the  reacting  mixture 
still  contain  about  25  per  cent  of  carbon  monoxid. 
These  are  drawn  off  just  below  the  top  of  the  furnace 
and  are  conducted  to  the  boiler  house,  where  they 
are  burned  to  generate  steam  for  the  engines  pro- 
ducing the  blast  of  air. 

423.  Varieties  of  Iron.     The  iron  we  use  and 
speak  of  is  not  pure,  but  contains  small  proportions 
of  other  elements  which  greatly  vary  its  properties. 


Iron,  Nickel,  and  Cobalt  309 

Carbon  has  the  greatest  influence  upon  the  proper- 
ties of  iron,  and  silicon  has  a  similar  but  less  intense 
effect.  Sulfur,  even  in  very  small  relative  amounts, 
makes  iron  brittle  when  hot,  and  hence  useless  for 
forging.  Phosphorus  renders  iron  brittle  at  ordi- 
nary temperatures.  Certain  metals,  notably  man- 
ganese, chromium,  and  nickel,  give  steel  some  very 
desirable  properties. 

424.  Cast  Iron.     Cast  iron  contains  from  2  to  7 
per  cent  of  carbon,  and  usually  2  to  3  per  cent  of 
other  elements.     If  most  of  the  carbon  is  chemi- 
cally combined  with  the  iron,  the  metal  is  known  as 
ivhite  cast  iron.     But  sometimes,  especially  when  the 
molten  metal  has  cooled  slowly,  some  of  the  carbon 
forms  graphite  which  imparts  a  darker  color  to  the 
iron,  which   is   hence   called  gray  cast  iron.      The 
latter  variety  is  softer  than  the  former  and  melts 
at  a  lower  temperature.     Cast  iron  is  too  brittle  to 
be  welded,  and  melts  at  a  much  lower  temperature 
than  pure  iron.     It  is  extensively  used  in  making 
castings.     For  that  purpose  it  is  melted  in  a  small 
blast  furnace,  and  the  molten  metal  poured  into 
sand  molds.     The  presence  of  manganese  makes 
it  coarsely  crystalline,  and  it  is  then  known  as  spie- 
gclciscn  or  fcrro-mangancsc. 

425.  Wrought  Iron.    Wrought  iron  is  prepared 
from  cast  iron  by  heating  it  in  puddling  furnaces. 
This  furnace  is  of  the  reverberatory  type  (Fig.  28), 
and  has  a  layer  of  ferric  oxid,  Fe2O3,  placed  tmder- 
neath  the  cast  iron.     As  the  flames  play  over  the 
mixture  the  cast  iron  melts  and  its  carbon  combines 
with  the  oxygen  in  the  oxid.      The  mixture  is  con- 
tinually  stirred   about   or   "puddled,"  and  as  the 


310  Elementary  Chemistry 

carbon  burns  out,  the  purified  iron,  melting  as  it  does 
at  a  higher  temperature  than  cast  iron,  becomes  of 
a  pasty  consistency.  The  puddler  shapes  the  pasty 
iron  into  large  balls  which  are  removed  from  the 
furnace  and  squeezed  in  rollers  or  hammered  into 
sheets.  Wrought  iron  is  also  made  by  the  open- 
hearth  process  (§429). 

Wrought  iron  contains  less  than  one-half  per 
cent  of  carbon.  It  is  tough  and  malleable  and  can 
be  forged  or  welded,  but  not  cast  or  tempered.  It 
is  often  called  malleable  iron,  and  is  made  into  wire 
nails,  bolts,  chains,  tires,  horseshoes,  and  so  on. 

426.  Steel.  Steel  contains  more  carbon  than 
wrought  iron,  but  less  than  cast  iron.  It  is  mallea- 
ble and  fusible,  and  can  be  forged,  welded,  and  cast. 
It  is  harder  than  wrought  iron  and  stronger  than 
cast  iron.  By  appropriate  treatment  it  can  be 
tempered,  i.  e.,  made  to  acquire  varying  degrees  of 
hardness.  If  steel  be  heated  to  a  red  heat  and  then 
suddenly  cooled  by  immersing  it  in  water  or  oil,  it 
becomes  less  malleable  but  much  harder,  and  can 
take  and  hold  a  sharp  edge.  If  such  tempered  steel 
be  heated  again  and  then  slowly  cooled,  it  becomes 
relatively  soft;  it  is  annealed ;  the  temper  is  "  drawn." 
Any  degree  of  hardness  may  be  obtained  between 
these  extremes.  Instruments  require  different  tem- 
pers according  to  their  application.  Thus,  ordinary 
cutlery  is  tempered  and  then  heated  to  about  250°, 
when  a  brown  film  of  oxid  appears ;  part  of  the  tem- 
per is  thereby  drawn  and  the  steel,  while  hard 
enough  for  cutting  purposes,  becomes  less  brittle. 
Watch-springs  after  tempering  are  heated  to  nearly 
300°,  when  a  blue  film  appears. 


Iron,  Nickel,  and  Cobalt  3 1 1 

427.  Manufacture  of  Steel.     As  it  is  the  car- 
bon contained  in  steel  which  mainly  determines  its 
properties,  the  aim  in  its  manufacture  is  to  give 
iron  the  desired  proportion  of  carbon,  and  at  the 
same  time  to  eliminate  such  substances  as  sulfur, 
phosphorus,  and  silicon,  which  impart  undesirable 
properties,  or  to  add  other  elements  as  manganese 
or  nickel,  which  give  certain  desirable  qualities  to 
the  steel.     In  the  cementation  or  crucible  process  bars 
of  wrought  iron  are  imbedded  in  finely  powdered 
charcoal  and  kept  at  a  red  heat  for  a  week  or  more. 
The  carbon  penetrates  the  iron,  producing  a  very 
fine  quality  of  steel,  especially  adapted  for  making 
tools.     The   expense   of   the   process,  however,    is 
prohibitive  for  most  purposes. 

NOTE.  Harveyized  steel  is  made  by  packing  steel  in  a  mix- 
ture of  charcoal  and  boneblack,  and  raising  to  a  high  temperature. 
This  operation  makes  the  outside  of  the  steel  very  hard,  so  chat  it 
is  adapted  for  armor  plate  for  war  vessels. 

428.  Bessemer  Process.      The  Bessemer  process 
consists  essentially  in  reducing  pig  iron  in  a  "  con- 
verter "to  wrought  iron,  and  then  adding  enough 
iron  containing  a  known  amount  of  carbon  to  bring 
the  proportion  of  carbon  up  to  the'desired  point. 

The  converter  (Fig.  38)  is  a  large  pear-shaped 
furnace  mounted  on  axes  or  trunnions  so  that  it 
may  be  inverted.  The  converter  is  made  of  iron 
plates  bound  together  and  lined  with  ganister,  a 
very  infusible,  siliceous  earth.  The  bottom  of  the 
converter  is  perforated  with  a  number  of  small 
holes,  up  through  which  a  blast  of  air  may  be 
forced.  A  charge  of  ten  to  twenty  tons  of  molten 
cast  iron  is  introduced  into  the  converter,  and  air 


3I2 


Elementary  Chemistry 


By  courtesy  of  the  SCIENTIFIC  AMERICAN 
Fig.   38 A  BESSEMER  CONVERTER  WHILE  THE   BLAST  IS  ON 

blown  up  through  it.  The  heat  generated  by  the 
burning  of  the  impurities  in  the  cast  iron  is  suffi- 
cient to  keep  the  metal  liquid,  and  in  about  half 
an  hour  it  is  converted  into  wrought  iron.  A 
weighed  amount  of  Spiegel  iron  is  now  thrown 


Iron,  Nickel,  and  Cobalt  313 

into  the  converter  and  in  a  few  moments  the  con- 
verter is  turned  over  and  the  steel  formed  run  out 
into  molds. 

BASIC-LINING  PROCESS.  Phosphorus  is  an  objection- 
able constituent  of  steel ;  hence  it  is  necessary  in  the 
Bessemer  process  to  employ  a  cast  iron  practically  free 
from  that  element.  It  may  be  removed,  however,  by 
lining  the  converter  with  a  mixture  of  lime  and  mag- 
nesia instead  of  ganister  ;  the  latter  is  acid,  while  the 
former  is  basic.  The  phosphorus  pentoxid  produced 
by  the  burning  unites  with  the  lime  and  magnesia, 
forming  phosphates  which  are  not  reduced  by  the  iron. 
Cast-iron  containing  phosphorus  may  therefore  be  used, 
as  the  phosphorus  is  thus  eliminated  from  the  steel. 
The  slag  (Thomas  slag)  obtained  consists  of  a  basic 
phosphate  which,  when  finely  ground,  has  great  value 
as  a  fertilizer. 

429.  Open-Hearth  Process.     Pig  iron  is  mixed 
with  wrought  iron  or  steel  scrap  and  heated  in  a 
reverberatory  furnace  with  an  oxidizing  gas  flame 
(Figs.  39  and  40).     When  enough  carbon  has  been 
burned  out,  Spiegel  iron  is  added,  or  about  every 
quarter-hour  a  sample  is  taken  from  the  furnace  and 
analyzed  for  carbon ;  the  operation  is  at  an  end  when 
the  right  amount  of  carbon  is  present.     The  steel 
made  by  this  process  is  very  tough  and  elastic,  so 
that  although  the  process  is  more  expensive  than 
the  Bessemer,  it  is  nevertheless  a  successful  rival. 

430.  Properties   of  Iron.     Physical.     (Table   L, 
Appendix  D.}    Pure  iron  is  a  silvery  white,  lustrous 
metal ;  it  is  the  most  magnetic  element,  losing  its 
•magnetism  readily,,  however,  while  steel  holds  it 
permanently. 

Chemical.  Chemically  pure  iron  is  prepared  by  re- 
ducing the  oxid  or  chlorid  in  a  current  of  hydrogen. 


314 


Elementary  Chemistry 


Fig.   39 FRONT  VIE\\ 


AX    OPEX-HEARTH    FURNACE 


When  this  reduction  takes  place  at  as  low  a  tem- 
perature as  possible,  the  iron  is  so  finely  divided 
that  it  takes  fire  when  exposed  to  the  air  at  ordi- 
nary temperatures;  it  is pyrophoric.  In  dry  air  iron 
is  not  affected,  but  in  moist  air  it  rusts,  forming 
ferric  hydroxid,  and  as  the  rust  does  not  form  a 
compact  protective  coating  to  the  iron,  the  latter  is 
in  time  totally  converted  into  the  former. 

As  water  dissociates  at  high  temperatures,  its 
oxygen  will  combine  with  red-hot  iron  to  form  the 
magnetic  oxid,  Fe3O4,  and  its  hydrogen  will  be  set 
free.  As  this  oxid  is  reduced  by  hydrogen,  a  state 
of  equilibrium  results : 

3Fe  +  4H2O^Fe304  +  4H2 

Iron  is  soluble  in  dilute  hydrochloric  and  sulfuric 
acids  with  evolution  of  hydrogen  and  formation  of 


Iron,  Nickel,  and  Cobalt 


315 


the  chlorid  and  sulfate,  respectively.  It  reduces 
rather  dilute  nitric  acid  with  formation  of  nitric 
oxid,  but  if  it  be  dipped  in  concentrated  nitric  acid 
and  then  rinsed  off,  it  is  not  acted  upon  by  the 
diluted  acid ;  it  is  converted  into  the  so-called  "  pas- 
sive state." 

COMPOUNDS  OF  IRON 

431.  Some  Important  Ferrous  and  Ferric  Com- 
pounds. Iron  forms  two  classes  of  compounds. 
It  is  bivalent  in  ferrous  compounds  and  trivalent  in 
ferric.  A  ferrous  compound  when  acted  upon  by 
an  oxidizing  agent,  such  as  oxygen,  nitric  acid,  or 
potassium  chlorate,  passes  into  the  corresponding 
ferric  compound,  and  this  in  turn  reverts  to  the 
original  ferrous  compound  when  acted  upon  by 
reducing  agents  such  as  hydrogen. 


Fig.  40 REAR  VIEW  OF  AN  OPEN-HEARTH  FURNACE 


316  Elementary  Chemistry 

432.  Oxids  and  Hydroxids.     Ferrous  oxid,  FeO, 
is  prepared  by  reducing  ferric  oxid  at  about  300°. 
It  is  a  black  powder  which  oxidizes  very  readily. 
Ferrous  hydroxid,  Fe(OH)2,  is  precipitated  by  the 
addition  of  an  alkalin  solution  from  ferrous  salt 
solutions.     It  is  of  a  pale  green  color,  but  oxidizes 
rapidly  into  brown  ferric  hydroxid. 

Ferric  oxid,  Fe2O3,  is  the  mineral  hematite. 
It  may  be  prepared  by  heating  ferric  hydroxid  or 
ferrous  sulfate,  and  forms  a  dark  red  powder/  It  is 
a  by-product  of  the  manufacture  of  fuming  sulfuric 
acid  and  of  galvanized  iron  and  tin  ware.  Under 
the  names  of  rouge  and  Venetian  red  it  is  used  to 
polish  glass  and  jewelry  and  to  make  red  paint. 

Ferric  hydroxid  is  thrown  down  as  a  reddish- 
brown  precipitate  when  ammonium  or  an  alkali 
metal  hydroxid  is  added  to  a  ferric  salt  in  solution. 
When  red-hot  iron  is  exposed  to  steam,  ferric  oxid 
is  formed ;  it  protects  the  iron  within  from  the  action 
of  the  weather. 

Ferrous-ferric  oxid,  Fe3O4,  occurs  as  the  mineral 
magnetite  (lodestone).  It  is  black  and  strongly 
magnetic,  hence  the  name  "  magnetic  oxid." 

433.  Iron  Sulfids.     Ferrous  sulfid,  FeS,  is  a  black 
solid   prepared   by   adding   an   alkalin   sulfid  to   a 
solution  of  a  ferrous  salt  or  by  heating  a  mixture 
of  iron  and  sulfur. 

Iron  pyrites,  FeS2,  is  of  the  color  of  brass.  Crys- 
tals of  it  are  often  found  in  rocks,  and  from  its 
often  being  taken  for  gold  it  has  received  the  pop- 
ular name  of  "  fool's  gold."  Its  sulfur  oxidizes  to 
sulfur  dioxid  when  it  is  heated ;  it  is  used  in  the 
manufacture  of  sulfuric  acid. 


Iron,  Nickel,  and  Cobalt  317 

434.  Iron   Chlorids.      Ferrous  chlorid,  FeCl2,  is 
formed  when  iron  interacts  with  hydrochloric  acid. 
It  crystallizes  from  solution  in  green  prisms  con- 
taining four  molecules  of  water.     It  may  be  pre- 
pared in  the  anhydrous  state  as  a  white  powder 
when  iron  is  heated  in  dry  hydrogen  chlorid. 

Ferric  cJilorid,  FeCl3,  is  formed  as  a  yellowish- 
brown  mass  when  chlorin  is  passed  over  red-hot 
iron.  It  is  very  deliquescent,  and  may  be  prepared 
in  solution  by  passing  chlorin  into  a  solution  of 
ferrous  chlorid. 

435.  Iron    Sulfates.     Ferrous  sulfatc,  FeSO4,  is 
formed  by  interaction  of  iron  or  ferrous  sulfid  with 
dilute  sulfuric  acid.     It  crystallizes  with  seven  mol- 
ecules of  water,  forming  green  crystals  known  as 
green  vitriol  or  copperas.     It  is  used  as  a  disinfectant, 
in  making  inks,  and  in  dyeing. 

Ferric  sulfate,  Fe2(SO4)3  is  obtained  in  solution 
by  the  oxidizing  action  of  nitric  acid  on  a  solution 
of  ferrous  sulfate. 

436.  Potassium     Ferro-    and     Ferri-Cyanids. 
Potassium  ferrocyanid,  K4Fe(CN)6  +  3  H2O   (yellow 
prussiate  of  potash)  forms  large  yellow  crystals  sol- 
uble in  water.     Heated  with  dilute  sulfuric  acid  it 
gives  prussic  acid,  and  with  concentrated  sulfuric 
acid,  carbon  monoxid.     When  its  solution  is  mixed 
with  that  of  a  ferric  salt,  a  precipitate  of  Prussian 
blue  is  obtained.    Prussian  blue  is  used  in  dyeing  and 
calico  printing,  and  in  making  bluing  and  blue  ink. 

Potassium  f err  icyanid,  K3Fe(CN)6  (red prussiate  of 
potas/i),  is  formed  from  a  solution  of  the  yellow 
prussiate  by  the  action  of  chlorin  or  bromin.  It  is 
an  important  constituent  of  blue-print  paper. 


318  Elementary  Chemistry 

NICKEL 

437.  Occurrence  and  Preparation.     Nickel,  like 
iron,  never  occurs  free  except  in  meteorites.     Its 
chief  ore  is  garnierite,  a  complex  silicate  which  is 
found  in  large  quantities  in  New  Caledonia.    Nickel 
is  obtained  from  this  ore  by  a  blast-furnace  process 
similar  to  that  used  in  obtaining  iron.     It  is  also 
obtained  by  electrolytic  processes. 

438.  Properties.     Physical.     (Table   L,   Appen- 
dix D.)     Nickel  is  almost  as  white  as  silver,  has  a 
brilliant  luster,  and  is  feebly  magnetic.      It  is  very 
tough  and  hard  and  may  be  welded  like  iron. 

Chemical.  Nickel  is  not  affected  by  the  air,  is 
acted  on  only  slowly  by  hydrochloric  and  sulfuric 
acids,  but  is  rapidly  dissolved  by  nitric  acid. 

439.  Uses.     Nickel  is  employed  in  nickel-plat- 
ing,  and    as    a    constituent    of   several    important 
alloys.    German  silver  contains  two  parts  of  copper 
and  one  each  of  nickel  and  zinc.    A  nickel  five-cent 
piece  contains  one  part  of  nickel  to  three  of  copper. 
Its  alloys  with  steel  (nickel  steel)  are  characterized 
by  great  hardness,  toughness,  and  durability,  and 
for  this  reason  are  used  in  making  armor  plate. 

440.  Some    Nickel    Compounds.     The   cldorid, 
NiCl2,    nitrate,   Ni(NO3)2,  and   sulfate,   NiSO4,  are 
green,  soluble  salts  made  by  dissolving  the  metal, 
its  oxid  or  hydroxid,  in  the  respective  acids.     The 
hydroxid,  Ni(OH)2,  is  thrown  down  from  solutions 
of  nickel  salts  by  the  addition  of  an  alkali,  as  a 
voluminous,  apple-green  precipitate,  which,  when 
heated,  loses  water  and  is  converted  into  nickel  oxid, 
NiO,  a  green  powder.     Nickel  sulfid,  NiS,  forms  a 
black  precipitate  when  a  soluble  sulfid  is  added  to 


Iron,  Nickel,  and  Cobalt 

a  solution  of  a  nickel  salt.  Nickel  car  bony  I,  Ni(CO)4, 
is  prepared  by  passing  carbon  monoxid  over  finely 
divided  nickel ;  it  is  a  colorless,  strongly  refracting, 
combustible  liquid,  which  boils  at  43°.  A  method 
of  extracting  nickel  from  low-grade  ores  is  based  on 
the  formation  of  nickel  carbonyL 

COBALT 

441.  Cobalt.  Cobalt  is  a  rare  element  found 
associated  with  nickel,  to  which  it  bears  a  close 
resemblance.  Cobalt  salts  are  blue  when  dry,  and 
red  when  dissolved  in  water.  A  solution  of  cobal- 
tous  chlorid,  CoCl2,  makes  a  good  sympathetic  ink. 
Smalt,  a  silicate  of  cobalt,  imparts  to  glass  a  beauti- 
ful blue  color. 

Exercises 

/.     What  is  the  object  of  painting  all  structural  iron  ? 

2.  Both  iron  and  aluminum  become  coated  with  their  respect- 
ive oxids  when  exposed  to  the  air.  Why  is  it  that  the  iron  gradu- 
ally is  entirely  "eaten  up  by  the  rust"  while  the  aluminum  is 
not  perceptibly  changed  ? 

j.  What  is  the  soluble  product  of  the  action  of  (a)  hydro- 
chloric acid  and  (ft)  sulfuric  acid  on  ferrous  sulfid  ? 

4.  What  objections  are  there  to  the  use  of  iron  pyrites  as  an 
ore  of  iron  ? 

jr.  Does  tinned  iron  rust?  Does  galvanized  iron  rust  ?  How 
can  you  account  for  the  difference  in  the  behavior  of  the  metallic 
coatings  ? 

Problems 

/.  Compute  which  has  the  larger  percentage  of  iron,  hematite, 
Fe2O3,  or  magnetite,  Fe3O4. 

2.  Iron  oxid,  Fe2O3,  contains  70  per  cent  of  iron  and  30  per 
cent  of  oxygen.  If  the  atomic  weight  of  oxygen  is  16.00,  what  is 
that  of  iron  ? 

j.  How  many  grams  of  ferrous  sulfid  are  needed  to  form 
enough  hydrogen  sulfid  to  precipitate  100^-  of  copper  sulfate  ? 


320  Elementary  Chemistry 


4.  Maumene,  in  1850,  reduced  12.  5  ^o^-  of  iron  oxid,  Fe2O3, 
by  heating  it  in  a  current  of  hydrogen  and  obtained  8.  7585  &•  of 
iron  ;  calculate  its  atomic  weight.  How  much  water  was  formed 
in  this  determination  ? 

j.  Berzelius,  in  1844,  dissolved  2.ggg^^-  of  iron  in  nitric  acid 
and  heated  the  nitrate  formed  until  it  was  converted  in  ferric  oxid, 
Fe2O3  ;  4.  2835  g-  of  the  oxid  were  obtained.  Find  the  atomic 
weight  of  iron. 

6.  Baubigny,  in  1883,  obtained  by  heating  n.754o<^-  of  nickel 
sulfate,  NiSO4,  5.1920^-  of  nickel  oxid,     The  atomic  weights  of 
oxygen  and  sulfur  are  16.00  and  32.06  ;  what  is  the  atomic  weight 
of  nickel  ? 

7.  Russell,  in  1869,  found  on  dissolving  nickel  in  hydrochloric 
acid  that  the  weight  of  the  hydrogen  was  3.411  per  cent  of  the 
weight  of  the  nickel.     Calculate  the  atomic  weight  of  nickel. 

8.  Russell,  in  1863,  reduced  28.5943^-  of  nickel  oxid  by  heat- 
ing in  hydrogen  and  obtained  22.5943<?".  of  nickel.     What  is  the 
atomic  weight  of  nickel  ? 

9.  Russell,   in    1869,   found   that   the   amount   of   hydrogen 
evolved  by  dissolving  cobalt  in  hydrochloric  acid  was  3.4017  per 
cent  of  the  metal.     Calculate  the  atomic  weight  of  cobalt. 


SVANTE  ARRHENIUS 
1859 i   Swede 

Originator  of  the  Theory  of  Elec- 
trolytic  Dissociation,    and  con- 
tributor to  the  Modern   Theory 
of  Solutions 


JACOBUS  HENRICUS  VAN'THOFF  WILHELM  OSTWALD 

1802 ;  Dutch  1853 ;   German 

Applied  the  gas  laws  to  solutions.  Ardent  advocate  of  the  Modern 

Studied  the  equilibrium  relation-  Theory  of  Solutions,   many  im- 

ships   of  solutions.    Founder  of  portant  deductions  from  which 

Modern  Theory  of  Solutions  he  has  drawn 


Plate  VII 


ARRHENIUS 


OSTWALD 


VAN*  T  HOFF 


Plate   VII 


CHAPTER  XXX 


CHROMIUM  AND  MANGANESE 

CHROMIUM 

442.  Occurrence  and  Preparation.   Chromium,  a 
rather  rare  element,  never  occurs  free,  and  is  prin- 
cipally found  in  chromite,  FeO'Cr2O3  (cJirome  iron 
stone),  and  in  crocoisitc,  PbCrO4  (lead  chromate).     It 
is   prepared   by   fusing   chromite   with   potassium 
hydroxid,  thus  forming  potassium  chromate,  from 
which  chromic  oxid,  Cr2O3,  may  be  obtained.   This 
can  be  reduced  by  heating  it  with  charcoal  in  an 
electric  furnace  or  by  the  action  of  aluminum. 

443.  Properties.     Physical.    (Table  I.,  Appendix 
D.)     Chromium  is  a  lustrous  metal  which  takes  a 
fine  polish.     It  is  very  hard  and  is  infusible  except 
at  the  temperature  of  the  electric  arc.    It  is  used  in 
the  manufacture  of  a  very  hard  steel,  called  chrome 
steel,  which  is  made  into  armor  plate,  projectiles, 
safes,  and  other  articles  that  require  great  power  of 
resistance. 

Chemical.  Nickel  is  unaffected  by  the  air.  It 
forms  three  sets  of  compounds ;  in  the  cliromoiis  and 
chromic  compounds  it  acts  as  a  base,  while  in  the 
cJiromates  it  behaves  as  an  acid-forming  element, 
resembling  sulfur  in  this  particular. 

444.  The   chromous   compounds   have  a  great 
tendency  to  become  oxidized  into  the  chromic  com- 
pounds, and  can  be  prepared  and  preserved  only 

[321] 


322  Elementary  Chemistry 

when  not  in  contact  with  air.  In  these  compounds 
the  chromium  is  bivalent,  as  chromous  oxid,  CrO, 
chromous  chlorid,  CrCl2 

445.  Chromic   Compounds.      Chromic  hydroxid, 
Cr(OH)3,  is  formed  as  a  green  precipitate  when  an 
alkalin  hydroxid  is  added  to  a  solution  of  a  chromic 
salt.    When  heated,  it  loses  water  and  is  converted 
into  chromic  oxid,  Cr2O3,  a  green  solid,  which  may 
also  be  prepared  by  heating  ammonium  chromate. 
When  fused  with  silicates,  it  colors  them  green,  and 
hence  is  used  for  coloring  glass  and  china. 

Chromic  sulfatc,  Cr2(SO4)3,  and  chromic  chlorid, 
CrCl3,  are  violet  solids  when  dry,  which  form  green 
solutions  from  which  green  crystals  containing 
water  of  crystallization  may  be  obtained. 

Chrome  alum,  Cr2(SO4)3'  K2SO4  +  24  H2O,  is  pre- 
pared by  passing  sulfur  dioxid  into  a  solution  of 
potassium  dichromate  containing  free  sulfuric  acid  : 

K2Cr207  +  H2S04  +  3S02 

-»  K2SO4-  Cr2(SO4)3  +  H2O 

It  forms  large  violet  crystals,  and  is  used  in  tan- 
ning and  dyeing. 

446.  Chromates.     There  are  numerous  salts  of 
the  type  M2CrO4,  which  are  derived  from  the  oxid 
CrO  3,  chromic  anhydrid.     The  corresponding  acid 
has  not  as  yet  been  isolated.     The  salts  of  chromic 
acid  are  analogous  to  those  of  sulfuric  acid. 

Chromic  anhydrid  is  obtained  by  the  action  of  sul- 
furic acid  on  a  strong  solution  of  potassium  dichro- 
mate, K2Cr2O7,  and  forms  long,  red,  needle-like 
crystals  which  are  very  soluble  in  water.  When 
heated  to  250°  it  decomposes  into  chromic  oxid  and 


Chromium  and  Manganese  323 

water.  It  is  so  powerful  an  oxidizing  agent  that  its 
solution  cannot  be  filtered  through  paper,  which  is 
destroyed  by  oxidation. 

The  alkali  chromates  are  prepared  by  fusing  chro- 
mate  with  an  alkalin  carbonate  and  extraction  with 
water.  Potassium  chromate  forms  yellow  crystals. 

The  bichromates  are  regarded  as  compounds  of 
a  chromate  with  chromic  anhydrid : 

K2CrO4  +  CrO3  -»  K2Cr2O7 

They  are  prepared  by  adding  sulfuric  acid  to  a 
solution  of  the  chromate. 

Potassium  dichromate  is  a  red,  soluble  salt,  fre- 
quently used  as  an  oxidizing  agent ;  it  is  reduced  to 
chromic  sulfate  when  heated  with  sulfuric  acid ;  the 
sulfate  of  potassium  also  is  formed,  and  some  of  the 
oxygen  is  made  available  for  oxidation. 

LEAD  CHROMATE,  PbCrO4,  is  a  yellow  solid,  formed 
when  potassium  chromate  or  dichromate  is  added  to  a 
solution  of  a  lead  salt.  It  is  used  under  the  name  of 
chrome  yelloiv  as  the  base  of  yellow  paint. 

MOLYBDENUM,  TUNGSTEN,  AND  URANIUM  are  rare 
metals  related  to  chromium.  Tungsten  is  used  to 
harden  steel,  ammonium  molybdate,  (NH4)2  MoO4,  is 
used  in  the  analysis  of  phosphorus  in  compounds;  and 
some  of  the  salts  of  uranium  when  fused  with  glass 
cause  it  to  appear  yellow  by  reflected  light,  and  green 
by  transmitted  light. 

MANGANESE 

447.  Occurrence  and  Preparation.  Manganese 
is  widely  diffused  in  nature,  never  occurring  free, 
however,  but  in  combination  as  oxid,  MnO2  (pyro- 
hisite),  and  Mn3O4  (Jiausmannite],  or  carbonate, 
MnCO3  (rJiodochrasitc).  It  is  prepared  by  reducing 
pyrolusite  in  an  electric  furnace. 


324  Elementary  Chemistry 

448.  Properties.    (Table  I.,  Appendix  Z>.)    Man- 
ganese is  very  lustrous  and  undergoes  a  superficial 
oxidation  so  that  it  has  an  iridescent  sheen.     It  is 
very  hard  and  infusible.     Alloys  of  manganese  and 
iron  (spiegel  iron  and  ferro  manganese)  are  exten- 
sively used  in  the  manufacture  of   steel.     When 
finely     divided,     manganese    decomposes    boiling 
water,  and  it  is  soluble  in  acids,  forming  manga- 
nous  salts. 

449.  Manganese  Compounds.    Manganese  forms 
several  series  of  compounds,  as  manganous  oxid, 
MnO,  manganic  oxid,  Mn2O3,  manganic  acid,  re- 
garded as  derived  from  an  anhydrid,  MnO3,  and 
permanganic    acid,    HMnO4,    derivable   from    the 
oxid,   Mn2O7.       In   some   way   the   compounds   of 
manganese,  especially  the  salts,  resemble  the  corre- 
sponding compounds  of  iron. 

450.  Oxids.     The  following  oxids  are  known : 
Manganous  oxid,   MnO,  a  green  powder,  oxidizing 
readily  to  the  higher  oxid,  Mn3O4  ;  manganic  oxid, 
Mn2O3,  a  dark  brown   powder;    mangano-manganic 
oxid,  Mn3O4  or  MnO'Mn2O3,  a  brownish-red  pow- 
der;   manganese  dioxid,  MnO2,  a  black  solid  (pyro- 
lusite);    and   manganese    kept  oxid,    Mn2O7,    a    dark- 
colored   liquid.      The   only  important   one   is   the 
dioxid,  which  is  used  in  making  chlorin  and  oxygen, 
in  decolorizing  glass,  and  in  manufacturing  steel. 

451.  Manganous  Salts.     The  salts  are  pink  in 
color,  soluble  in  water,  and  behave  like  those  of 
magnesium  and  iron.     Manganous  sulfid,  MnS,  is  a 
flesh-colored  precipitate  formed  when  ammonium 
sulfid  is  added  to  a  solution  of  a  manganous  salt,  as 
the  chlorid,  MnCl2,  or  sulfate,  MnSO4. 


Chromium  and  Manganese 


325 


452.  Manganates  and  Permanganates.  When 
manganese  compounds  are  fused  with  potassium 
hydroxid  in  the  presence  of  air,  or  better,  of  some 
oxidizing  agent,  as  potassium  nitrate  or  chlorate,  a 
green  mass  results,  which  forms  a  dark-green  solu- 
tion of  potassium  manganate,  K2MnO4.  When  this 
solution  is  boiled  and  carbon  dioxid  or  chlorin 
passed  into  it,  potassium  permanganate,  KMnO4,  is 
formed. 

3K2MnO4+2CO2->2K2CO3  +  2KMnO4  +  MnO2 
2  K2MnO4  +  C12  — >  2  KC1  +  2  KMnO4 

Potassium  permanganate  forms  hard,  greenish- 
black  crystals,  which  dissolve  in  water  to  form  a 
deep  purple  solution.  This  solution  acts  as  a  pow- 
erful oxidizing  agent,  and  is  used  on  a  large  scale 
to  purify  water  and  sewage.  It  is  also  used  in 
medicine,  in  bleaching  and  dyeing,  and  in  staining 
wood. 

Problems 

/.  Ramson,  in  1889,  heated  6.65949^"-  of  ammonium  dichro- 
mate,  (NH4)2Cr2O7,  and  obtained  4.oi87i<?"-  of  chromium  trioxid, 
Cr2O3.  Taking  the  atomic  weights  of  nitrogen,  hydrogen,  and 
oxygen  as  14.041,  1.008,  and  16.000,  respectively,  calculate  the 
atomic  weight  of  chromium. 

2.  Siewert,  in  1861,  found  that  'j.dgigg'-  of  silver  chlorid  were 
obtained  by  the  action  of  silver  nitrate  on  a  solution  containing 
2.8338<?"-  of  chromium  chlorid,  CrCl3.  Knowing  that  the  atomic 
weights  of  silver  and  chlorin  are  35.45  and  107.94,  respectively, 
what  is  that  of  chromium  ? 

j.  Marignac,  in  1884,  converted  io.6647<£r-  of  manganous  oxid, 
MnO,  into  22.6875^-  of  manganous  sulfate,  MnSO4.  Taking  the 
atomic  weights  of  sulfur  as  32.06,  and  of  oxygen  as  16.00,  find  the 
atomic  weight  of  manganese. 


CHAPTER  XXXI 


THE  PERIODIC  SYSTEM 

453.  Retrospect.     In  our  foregoing  study  of  the 
elements  we  have  found  that  they  could  be  classed 
into  groups,  the  members  of  which  were  similar  as 
regards  their  valence,  physical  properties,  and  chem- 
ical behavior.     We  found  also  that  in  the  case  of 
certain  groups  of  three  elements  there  was  a  simple 
relationship  between  their  atomic  weights,  for  the 
half  of  the  sum  of  the  smallest  and  largest  atomic 
weight   equaled   the   intermediate    atomic   weight 
(page    198).     In    1865,  Newlands,   an   Englishman, 
proposed  his  Law  of  Octaves;  he  had  found  that 
if  the  elements  are  arranged  in  the  order  of  their 
atomic  weights,  the  eighth,  fifteenth,  etc.,  elements 
exhibited  properties  similar  to  those  of  the  first 
element.     And  about  five  years  later,  the  Russian, 
Mendeleeff,  and  the  German,  Lothar  Meyer,  inde- 
pendently extended  these  observations  and  arrived 
at  conclusions  embraced  by  the  term  "  Periodic  Law." 

454.  Development  of  the  System.     If  we  write 
the  symbols  of  the  elements  in  the  order  of  their 
increasing  atomic  weights,  beginning  with  lithium 
and  ending  with  chlorin,  we  have : 

Li,  7  ;       Be,  9;       B,  u  ;     C,  12  ;        N,  14  ;  O,  16  ;  F,  19 
Na,  23  ;   Mg,  24  ;   Al,  27  ;    81,28.4;    P,  31  ;   8,32;    €1,35.5 

We  see  that  while  there  is  a  gradual  change  in  the 
properties  of  the  elements  in  the  same  horizontal 

[326] 


The  Periodic  System  327 

line,  there  is  a  sudden  change  in  passing  from  the 
end  of  the  first  line  to  the  beginning  of  the  second ; 
fluorin  and  sodium  have  opposite  properties.  We 
note,  moreover,  that  the  elements  in  the  same  ver- 
tical columns  exhibit  close  similarities,  and  indeed 
are  members  of  the  groups  of  elements  we  have 
been  studying. 

The  regular  gradation  of  such  properties  as 
valence  and  specific  gravity  is  shown  in  the  follow- 
ing table : 

Element..  Na    Mg    Al      Si       ?(red)  S  Cl(//?.) 

Valence..  I.  II.  III.  IV.  (V.  &  VII.)  (II.  IV.  &  VI.)  (I.  &  VII.) 
Sp.  Grav.o.gj  1.75  2.67  2.49  2.14  2.06  1.33 

Furthermore,  if  we  write  down  the  symbols  of  a 
series  of  elements  according  to  their  increasing 
atomic  weights,  beginning  with  another  univalent 
metal,  as  silver,  for  instance,  and  placing  the  atomic 
weights  and  specific  gravities  under  the  symbols, 

we  have : 

Ag'  Cd"  Zn'"  Sn""  Sb'"  Te"  T 

Atom.  Wt.       108  112.4  JI4  118.5  120  127  126.9 

Sp,  Grav.      10.5  8.6  7.4  7.2  6.7  6.2  4.9 

Reading  from  left  to  right  we  see  a  regular  change 
of  properties,  and  if  this  series  be  written  down 
below  the  two  preceding  ones  we  have : 

Li,  7;   Be,  9.1;   B,  ii  ;   C,  12  ;    N,  14  ;   O,  16  ;   F,  19 
Na,  23  ;  Mg,  24.4;  Al,  27.1  ;  Si,  28.4;  P,  31  ;   8,32;   €1,35.5 
Ag,  108  ;  Cd,  112.4  ;  Zn,  114  ;  Sn,  118.5  ;  Sb,  120  ;  Te,  127  ;  I,  126.9 

We  observe  that  the  elements  in  the  same  vertical 
column  belong  to  a  natural  group,  as  that  of  the 
alkali  metals  or  the  halogens. 

These  and  other  facts  lead  to  the  conclusion  that 
the  properties   of  the   elements   stand  in   a   close 


328  Elementary  Chemistry 

relationship  to  their  atomic  weights.  Moreover, 
there  are  UL  the  series  regular  recurrences  of  ele- 
ments of  similar  properties  at  intervals  of  about  16. 
In  the  language  of  mathematics,  when  one  quantity 
stands  in  such  a  relationship  to  another  that  when 
one  changes  the  other  also  changes,  the  one  is  said 
to  be  a  function  of  the  other,  and  when  as  one  quan- 
tity increases  uniformly  the  other  assumes  at  regular 
intervals  the  same  value,  the  function  is  said  to  be  a 
periodic  one.  Borrowing  then  this  mode  of  expres- 
sion we  may  say : 

The  properties  of  the  elements  are  periodic  functions  of 
their  atomic  weights.  This  statement  is  known  as  the 
Periodic  Law.  The  arrangement  of  the  elements  in 
these  periods  is  shown  in  the  table  opposite. 

455.  Large  and  Small  Periods.     In  the  period 
beginning  with  potassium,  it  is  seen  that  after  man- 
ganese, the  seventh  member,  there  occur  three  quite 
similar  elements,  iron,  nickel,  and  cobalt,  which  do 
not  fit  under  potassium,  calcium,  and  scandium.    In 
order  to  have  the  next  period,  which  begins  with 
copper,  correspond  with  the  preceding  period,  it  is 
necessary  to  place  iron,  nickel,  and  cobalt  in  an 
intermediate  group  by  themselves.     After  the  first 
two  periods  of  seven  elements  each,  comes  one  of 
seventeen  elements,  made  up  of  two  small  periods 
of  seven  elements  each  and  three  elements  inter- 
mediate.    A  similar  long  period  occurs  also  farther 
on  in  the  table. 

456.  The  Value  of  the  Periodic  Law  consists  in 
the  following  facts : 

i .  It  gives  a  systematic  classification  of  the  ele- 
ments, which  is  nearly  free  from  arbitrariness. 


»g     3 


o 

•^    I 


Crq  c 
o<? 


2? 


CfQ 


s? 


r 

to  cr     P 

O     M  M 


dd 


M°, 
»P 


o 


0     X 


to  P        ^' 


c 


(T>   O 

MO 

to  o^ 

o 


CD    -j 
•>J  <j\ 

vO    to 


Q 
ga 


:   i 


330  Elementary  Chemistry 

2.  It  assists  in  the  fixing  of  the  atomic  weights 
of  such  elements,  only  the   equivalent  weights  of 
which  can  be  determined. 

3.  It  furnishes  a  means  of  predicting  the  prop- 
erties of  elements  as  yet  not  discovered. 

4.  It  may  be  employed  to  confirm  or  correct  the 
atomic  weights  of  elements  which  may  be  doubtful. 

Illustrations  of  the  second  and  third  items  of 
value  of  the  law  are  too  difficult  for  an  elementary 
book,  but  it  may  be  stated  that  they  have  been 
applied  in  several  cases  with  complete  success. 

457.  Classification  of  the  Elements.     The  phys- 
ical and  chemical  properties  of  an  element  may  be 
ascertained  from  the  position  it  occupies  in  the  sys- 
tem and  particularly  by  the  four  adjacent  elements, 
its  analogues.    Thus,  if  the  properties  of  magnesium 
were  unknown,   they   could   be  deduced  approxi- 
mately from  those  of  its  four  analogues  —  sodium, 
beryllium,  aluminum,  and  calcium.     For  instance, 
its  atomic  weight  is  very  nearly  the  average  of  the 
atomic  weights  of  its  analogues. 

23+9  +  27  +  40 

—  =  2475 
4 

Also,  its  specific  gravity,  by  experiment  found  to 
be  1.75,  is  about  the  average  of  tho,  specific  grav- 
ities of  its  analogues : 

0.97  +  2.10+2.56+1.58 

—  I.QO 

4 

458.  Prediction  of  Unknown   Elements.     The 

blanks  or  gaps  in  the  table  represent  the  positions 
of  elements  as  yet  undiscovered.  When  the  table 


The  Periodic  System  331 

was  first  drawn  up,  the  number  of  blanks  was 
greater  than  now,  and  Mendeleeff  did  not  hesitate 
to  prophesy  the  existence  of  elements  to  fill  the 
gaps,  and  even  predicted  the  properties  which  they 
should  possess.  His  predictions  have  been  fulfilled 
in  several  cases.  The  three  elements,  gallium, 
germanium,  and  scandium,  have  all  been  discovered 
since  his  formulation  of  the  law,  and  have  been 
found  not  only  to  naturally  fall  into  the  places  he 
had  assigned  them,  but  also  to  present  very  closely 
the  physical  and  chemical  properties  he  had  pre- 
dicted for  them.  The  filling  up  of  all  the  gaps 
now  present  in  the  table  is  probably  but  a  matter 
of  time.  It  should  be  stated,  however,  that  the 
system  did  not  in  the  least  lead  chemists  to  suspect 
the  existence  of  the  elements,  helium  and  argon,  to 
which,  indeed,  it  is  found  difficult  to  assign  satis- 
factory places  in  the  table.  The  system  certainly 
has  faults,  but  is  full  of  suggestions,  the  following 
up  of  which  has  led  to  important  discoveries.  The 
formulation  of  the  Periodic  Law  has  been  a  decided 
help  to  the  advance  of  chemical  knowledge,  and 
undoubtedly  paves  the  way  towards  a  deeper  insight 
into  the  nature  and  relationships  of  the  different 
kinds  of  matter,  if  not  into  the  nature  of  matter 
itself, 


CHAPTER  XXXII 

SOME  COMMON  ORGANIC  COMPOUNDS 

The  distinction  between  organic  chemistry  and 
inorganic  chemistry  has  already  been  made  clear 
(§  100).  Since  many  of  the  compounds  of  carbon 
are  in  everyday  use,  mention  of  their  occurrence, 
preparation,  and  properties  will  be  made  in  the 
following  pages,  although  nothing  like  a  thorough- 
going and  systematic  treatment  will  be  attempted. 

459.  Composition  of  Carbon  Compounds.      Al- 
though  the   number   of   compounds   of   carbon   is 
greater  than  the  number  of  compounds  of  all  the 
other  elements,  yet  comparatively  few  elements  are 
combined   with   carbon   to   form   the  majority   of 
these  compounds.    Hydrogen,  oxygen,  and  nitrogen 
are  the  most  frequently  occurring  elements  in  car- 
bon compounds  as  they  occur  in  nature,  although 
phosphorus  and  sulfur  are  not  uncommon.    Carbon 
compounds  made  in  the  laboratory  may  contain  any 
element ;  the  halogens  are  especially  common. 

460.  The   Valency   of  Carbon ;    Graphic    For- 
mulas.    Carbon  is  quadrivalent  in  most  of  its  com- 
pounds;  carbon  monoxid,  in  which  it  is  bivalent, 
is  a  familiar  exception.     The  quadrivalency  of  car- 
bon is  the  corner  stone  of  the  edifice  of  organic 
chemistry. 

It  is  customary  to  bring  out  the  valencies  of  ele- 
ments by  writing  their  symbols  in  connection  with 
dashes  equal  in  number  to  their  valence.  Thus : 

[332] 


Some  Common  Organic  Compounds  333 

_C-  -N-  -O-  H- 

i  i 

The  formulas  of  methane,  ammonia,  water,  and 
hydrogen  expressed  accordingly  are  : 

H 

H-C-H         H-N-H         H-O-H        H-H 

i  i 

H  H 

The  formulas  of  the  two  first  chlorin  substitu- 
tion products  of  methane  (page  171)  are 

H  H 

H-C-C1  H-C-C1 

i  i 

H  Cl 

(methyl  chlortd}  (methylene  chlorid} 

461.  The  Nature  of  Carbon.  The  large  num- 
ber of  carbon  compounds  is  due  chiefly  to  the  val- 
ency of  carbon  and  its  behavior  toward  itself. 
This  behavior  may  be  summed  ut>  in  the  following 
statements : 

/.  Several  carbon  atoms  may  be  joined  by  one, 
two,  or  three  valencies,  as  C-C,  C  =  C,  C  =  C. 

2.  Several  carbon  atoms  may  unite  so  as  to 
form  the  so-called  " carbon  chains,"  as  C-C-C-C, 
C-C-C-C-C,  C-C-C-C.  The  number  of  atoms 
thus  linked  together  has  been  found  to  be  as  large 
as  thirty. 

j.  The  "carbon  chains"  may  be  open  or  closed. 
Open  chains  have  separate  atoms  at  each  end,  as 
shown  in  2,  while  in  the  closed  chains  those  atoms 


334  Elementary  Chemistry 

which  would  be  the  first  and  the  last  atoms  in  the 

closed  chain  unite  so  as  to  form  a  ring,  thus : 

^C.  .C      ^C 

c      c  c               c      c      c 

II  /         N                                    III 

C         C  C-C                  C         C         C 


^.  Molecules  of  carbon  compounds  may  contain 
both  open  and  closed  chains : 

Co    o  ^  C  >-    ^  C 

-   <v-t>  „         „ 

C        C  C        C 

II 

C         C-C-C-C  C         C-C-C 

-er  ^c' 

5.  Other  elements,  excepting,  of  course,  univa- 
lent  elements,  may  take  part  in  the  formation  of 
both  open  and  closed  chains : 

C-CN  C-CN  ,C-CX 

N-  |          S  c  N- 

c-c7  c-cx  xc-cx 

462.  Radicals.  We  have  learned  (§135)  that 
there  are  certain  groups  of  atoms  which  are  found 
repeating  themselves  in  numerous  compounds 
derived  from  one  another  and  which  play  in  these 
compounds  the  part  of  an  atom.  For  instance, 
methyl,  -CH3,  and  methylene,  =CH2,  in  the  formulas 
on  page  333,  are  simple  and  common  radicals.  They 
have  never  been  isolated ;  all  attempts  at  isolation 
have  resulted  in  the  formation  of  the  compounds 
H3C-CH3  (ethane,  C2H6)  and  H2C-CH2  (ethylene 
C2H4). 


Some  Common  Organic  Compounds  335 

463.  Isomerism  and  Polymerism.     Ethane  and 
ethylene  have  molecular  weights  twice  as  large  as 
methyl  and  methylene.     Methyl  and  methylene  are 
said  to  polymerise  and  form  ethane  and  ethylene ; 
and  methyl  and  ethane,  and  methylene  and  ethylene 
are  said  to  be  polymers  of  each  other.      Polymers 
then  are  substances  which  have  the  same  percentage 
composition,  but  different  molecular  weights  and 
properties. 

There  are  also  many  substances  which  have 
the  same  percentage  composition  and  the  same 
molecular  weight,  but  which  have  quite  different 
properties.  Their  molecules  are  made  of  equal 
numbers  of  the  same  atoms.  The  differences  in 
properties  then  must  be  due  to  differences  in  the 
arrangement  of  the  atoms  in  the  molecule.  Such 
compounds  are  called  isomcrs. 

464.  Classification    of   Carbon    Compounds. 
Only  the  most  common  of  the  numerous  classes  of 
compounds  of  carbon  can  be  mentioned  here,  such 
as    (i)    hydrocarbons,    (2)   alcohols,   (3)   aldehydes, 
(4)  ethers,  (5)  acids,  (6)  esters,   (7)   carbohydrates, 
(8)  benzene  derivatives. 

HYDROCARBONS 

Hydrocarbons  have  already  been  considered  in 
Chapter  IX.  Some  additional  ones  will  be  discussed 
under  Benzene  Derivatives  (§487). 

ALCOHOLS 

The  alcohols  may  be  regarded  as  hydroxids  of 
certain  radicals,  such  as  methyl  and  ethyl.  They 
behave  like  bases  in  that  they  combine  with  acids, 
with  elimination  of  water,  to  form  compounds 


336  Elementary  CJiemistry 

analogous  to  salts  in  constitution ;  the  latter  com- 
pounds are  termed  esters  or  ethereal  salts. 

465.  Methyl  Alcohol,  CH3OH.     Methyl  alcohol 
is  one  of  the  products  of  the   dry  distillation  of 
wood,  and  for  that  reason  is  often  called  wood  alcohol 
or  wood  spirit.     It  is  a  colorless  liquid  with  a  spirit- 
uous odor  and  burning  taste.     It  mixes  with  water 
in  all  proportions.     It  is  used  as  a  solvent  for  oils, 
fats,  and  shellac,  and  in  the  manufacture  of  varnishes. 

466.  Ethyl    Alcohol,    C2H5OH.     Ethyl   alcohol 
is  prepared  by  the  action  of  yeast  on  a   solution 
containing   glucose;     carbon   dioxid   (§  89)   is    the 
other  main  product.    The  reaction  during  fermenta- 
tion may  be  represented  by  the  equation: 

C6H1206  =2C2H60      +      2C02 

(glucose}  (alcohol}  (carbon  dioxid} 

When  the  fermenting  solution  contains  some- 
thing over  10  per  cent  of  alcohol,  the  fermentation 
ceases,  i.  e.,  the  yeast  plant  stops  multiplying.  The 
solution  is  then  filtered  and  concentrated  by  distil- 
lation. 

Ethyl  alcohol  is  a  colorless  liquid,  having  a 
spirituous  odor  and  a  burning  taste.  It  is  miscible 
in  all  proportions  with  water.  The  ordinary  com- 
mercial article  contains  from  5  to  10  per  cent  of 
water;  proof  spirit  contains  50  per  cent  of  water. 
Pure  or  absolute  alcohol  is  prepared  by  distilling 
ordinary  alcohol  over  lime  or  calcium  carbid  to 
remove  the  water. 

As  alcohol  is  a  good  solvent  for  most  oils,  gums, 
and  resins,  it  is  extensively  used  in  the  manufacture 
of  essences,  extracts,  tinctures,  varnishes,  and  medi- 
cines. It  is  employed  as  an  antiseptic,  as  a  source 


Some  Common  Organic  Compounds  337 

of  heat  in  alcohol  lamps,  and  as  a  preservative  for 
anatomical  specimens  in  museums.  It  is  often  con- 
verted into  vinegar  (§  473),  and  many  organic  com- 
pounds require  its  use  in  their  preparation. 

467.  Alcoholic   Liquors,     The   juices   of   fruits 
when  exposed  to  the  air  receive  ferments  (fungi 
capable  of  producing  fermentation)  from  it  and,  if 
the  conditions  are  right,  go  through  the  process  of 
fermentation.     This  fermented  juice   forms   wine. 
Grain  also  when  soaked  in  water  containing  malt 
(barley  which  has  sprouted)  undergoes  fermenta- 
tion, and,  when  hops  are  added  to  the  fermented 
liquor,  beer  is  the  product.     Wine  and  beer  then  are 
for  the  most  part  mixtures  of  alcohol  and  water,  but 
with  numerous  other  substances  present  which  give 
each  liquor  its  peculiar  properties.     Beer  contains 
from  3  to  7  per  cent  of  alcohol;  wine  from  6  to  20 
per  cent. 

When  wine  is  distilled  the  distillate  is  known  as 
brandy.  Likewise,  the  distillation  of  the  liquors  in 
which  the  fermentation  of  substances  such  as  grain 
or  molasses  has  taken  place,  yields  other  distilled 
liquors,  such  as  whisky,  gin,  or  rum. 

468.  Glycerin,    C,H5(OH)3.     While    ethyl    and 
methyl  alcohols  contain  but  one  hydroxyl  group, 
glycerin   contains   three,    so  that  its  chemical  be- 
havior is  correspondingly  complex.     The  method 
of  preparation  of  glycerin  will  be  described  under 
Soap  (§  480). 

Glycerin  is  a  thick,  colorless,  odorless  liquid 
with  a  sweet  taste.  It  is  miscible  with  both  water 
and  alcohol,  and  absorbs  moisture  from  the  air.  It 
is  used  in  the  manufacture  of  copying  inks,  toilet 

23 


338  Elementary  Chemistry 

soaps,  printers'  ink  rollers,  and  nitroglycerin ;  it  is 
also  used  as  a  solvent,  a  lubricator,  a  cosmetic,  as 
sweetening  in  certain  liquors,  preserves,  and  candy, 
and  as  an  adulterant  for  molasses, 

ALDEHYDES 

When  alcohols  are  oxidized  under  certain  con- 
ditions, aldehydes  are  formed ;  these  may  be  re- 
garded as  compounds  of  the  aldehyde  radical,  CHO, 
with  other  organic  radicals. 

469.  Formaldehyde,  HCHO.     Formaldehyde  is 
a  gas  with  a  penetrating  odor ;  it  is  readily  soluble 
in  water.     It  is  used  extensively  as  a  disinfectant 
and  a  food  preservative.     A  solution  containing  40 
per  cent  of  formaldehyde  is  known  as  formalin. 

470.  Acetaldehyde,  CH3CHO.    Acetaldehyde  is 
obtained  by  partially  oxidizing  alcohol. 

C2H5OH  +  O  =  CH3CHO  +  H2O 
It  is  a  colorless  liquid  with  a  suffocating  odor.     It  is 
a  powerful  reducing  agent,  and  is  sometimes  used 
to  precipitate  silver  as  a  coating  on  glass  in  making 
mirrors. 

When  alcohol  is  oxidized  with  chlorin,  chloral, 
CC13CHO,  is  produced.  Chloral  forms  with  water 
cJdoral  Jiydrate,  CC13CHO  °  H2O,  a  compound  often 
used  to  ease  pain  and  induce  sleep.  Chloral  in 
alkalin  solution  forms  cJdoroform,  CHC13,  the  well- 
known  anaesthetic.  lodoform,  CHI3,  which  is  the 
iodin  compound  corresponding  to  chloroform,  is  a 
yellow  solid  with  a  disagreeable  odor.  It  is  used  as 
a  surgical  dressing. 

NOTE.  The  word  aldehyde  is  intended  to  show  that  <?/cohol  is 
<7^XrK</rogenated  to  produce  it.  The  prefix  acet  indicates  that  acet- 
aldehyde  when  oxidized  yields  acetic  acid. 


Some  Common  Organic  Compounds  339 

ETHERS 

Ethers  may  be  regarded  as  oxids  of  hydrocarbon 
radicals.  They  are  prepared  by  removing  one 
molecule  of  water  from  two  molecules  of  an  alcohol. 

471.  Ethyl   Ether,  (C2H5)2O.      Ethyl  ether  is 
prepared  by  heating  alcohol  with  the  dehydrating 
agent,  concentrated  sulfuric  acid: 

C2H5  OH        HO     >  C  2  H  ,  \  Q 
C2HS  OH  '     H*U    ^C2H3/ 

Ether  is  a  colorless  liquid  with  a  peculiar  and 
rather  pleasant  taste  and  odor.  It  is  very  volatile 
and  as  its  vapor  is  very  inflammable,  it  should  not 
be  brought  near  a  flame.  It  is  miscible  with  water 
only  to  a  limited  extent.  Its  chief  use  is  as  an 
anaesthetic. 

ACIDS 

Organic  acids  are  compounds  of  certain  organic 
radicals  with  car  boxy  I,  CO2H.  They  may  be  pre- 
pared by  oxidation  of  the  corresponding  alcohols. 

H  H  H 

H-C-H         H-C-OH  C  =  O   O  =  C-O-H 

H-C-H         H-C-H        H-C-H      H-C-H 

(ill 

H  H  H  H 

(ethane)  (ethyl  alcohol}     (acetaldehyde)    (acetic  acid} 

472.  Acetic  Acid,   CH2CO2H.      Acetic   acid  is 
one  of  the  products  of  the  destructive  distillation  of 
wood.     The  distillate  (called  pyroligneous  acid}  is  a 
dark  red  liquid  containing  about   10   per  cent   of 
acetic  acid,   together  with  smaller  proportions  of 
methyl  alcohol  and  numerous  other  organic  com- 
pounds.    When  this  acid  distillate  is  neutralized 


340  Elementary  Chemistry 

with  lime  or  soda,  calcium  or  sodium  acetate  is 
formed.  This  is  then  heated  with  sulfuric  acid; 
acetic  acid  is  thus  freed  from  the  base  and  collects 
as  a  distillate  mixed  with  about  70  per  cent  of 
water.  By  expelling  the  water  of  crystallization 
from  sodium  acetate  before  distilling  it  with  sul- 
furic acid,  a  very  concentrated  acetic  acid  is  ob- 
tained; this  is  called  glacial  acetic  acid  because  it 
solidifies  at  17°. 

Acetic  acid  is  a  colorless  liquid  with  a  pungent 
odor  and  sharp  taste.  It  is  miscible  in  all  propor- 
tions with  water. 

ACETATES.  Acetic  acid  is  monobasic  and  forms  the 
series  of  salts  known  as  acetates,  some  of  which  are 
important. 

Sodium  acetate,  NaC2H3O2  -f-  3H2O,  forms  white 
crystals.  It  is  used  in  the  manufacture  of  pure  acetic 
acid  and  in  making  certain  dyes. 

Lead  acetate,  Pb  (C2H3O2)2,  is  a  white  solid  used  in 
dyeing  and  in  making  a  yellow  paint. 

Aluminum  acetate,  although  not  known  in  a  state  of 
purity,  is  used  in  an  impure  state  when  in  solution 
(known  as  "red  liquor  ")  for  dyeing  and  calico  printing. 

Iron  acetate  is  used  in  solution  in  dyeing  silks  and 
cottons  black.  The  solution  is  black  and  is  known  as 
"iron  liquor." 

Verdigris  is  a  complex  copper  acetate  used  in  manu- 
facturing blue  paint. 

Paris  green  is  another  complex  acetate  of  copper 
and  arsenic  (page  248). 

473.  Vinegar.  Vinegar  is  dilute,  impure  acetic 
acid,  prepared  by  the  oxidation  of  weak  alcohol. 
The  oxidation  is  effected  by  fermentation.  Thus, 
cider,  beer,  and  weak  wines  become  sour  when 
exposed  to  the  air  in  a  warm  place,  because  a  certain 
ferment  flourishes  in  them,  changing  the  alcohol  to 


Some  Common  Organic  Compounds  341 

acid.     Strong  wine  and  pure  dilute  alcohol  do  not 
sour,  because  the  ferment  cannot  grow  in  them. 

Vinegar  is  manufactured  by  soaking  wood  shavings 
in  vinegar  ferment,  placing  them  in  a  cask  with  numer- 
ous holes  punched  in  it  so  as  to  give  free  access  to  the 
air,  and  allowing  dilute  wine,  cider,  or  alcohol  to  trickle 
down  over  them.  The  ferment  acts  rapidly  upon  the 
alcohol  thus  spread  out  over  the  shavings,  and  the  liquor 
after  two  or  three  such  treatments  is  converted  into 
vinegar. 

474.  Oxalic  Acid,  C2H2O4+ 2  H2O.    Oxalic  acid, 
combined    with    calcium,   occurs    in   rhubarb   and 
sorrel.     It  is  manufactured  by  heating  sawdust  and 
caustic  potash  together,  and  treating  the  residue 
with  lime.     The  calcium  salt  is  then  decomposed 
by  heating  with  sulfuric  acid. 

Oxalic  acid  forms  white,  soluble  crystals,  which 
are  very  poisonous.  Its  use  in  removing  ink  spots 
and  iron  rust  from  clothing  is  well  known.  The 
acid  and  its  salts  are  also  extensively  employed  in 
dyeing,  calico  printing,  photography,  and  in  the 
manufacture  of  dyes. 

475.  Lactic    Acid,    C3H6O3.     Lactic    acid   is  a 
product  of  the  fermentation  of  milk  sugar,  and  is 
hence  found  in  sour  milk.     It  forms  a  thick,  sour 
liquid,   readily  decomposed  by  heat.     Lactic  acid 
and  some  of  its  salts  are  used  in  medicine,  and  in 
dyeing  and  calico  printing, 

476.  Tartaric  Acid,   C4H6O6.     The  potassium 
salt  of  tartaric  acid  occurs  in  grapes  and  other  fruits. 
When  grape  juice   ferments,  this   acid   potassium 
tartrate  separates  from  its  solution  and  collects  on 
the  bottom  of  the  casks.     This  crude  tartar  or  argol 


342  Elementary  Chemistry 

is  converted  into  pure  tartaric  acid  by  treating  it 
with  chalk  and  then  with  sulfuric  acid.  Tartaric 
acid  forms  large,  transparent  crystals,  soluble  in 
both  water  and  alcohol.  It  is  the  acid  ingredient 
of  a  Seidlitz  powder,  the  other  being  sodium  bicar- 
bonate. 

When  acid  potassium  tartrate  is  purified,  it  is 
known  as  cream  of  tartar,  and  is  used  in  making 
baking  powder  (page  195).  Tartar  emetic  is  a  tartrate 
of  potassium  and  antimony ;  it  is  used  in  medicine. 

MALIC  ACID,  C4H6OS.  Malic  acid  is  found  free  and 
in  the  form  of  salts  in  many  fruits.  It  is  a  white,  crys- 
talline solid,  soluble  in  water. 

CITRIC  ACID,  C6H8O7.  Citric  acid  occurs  free  in 
lemons  and  oranges,  and  in  a  much  smaller  quantity  in 
currants  and  gooseberries.  It  forms  white  crystals, 
readily  soluble  in  water.  It  gives  the  sour  taste  to 
lemonade,  and  its  salt,  magnesium  citrate,  is  used  in 
medicine. 

BUTYRIC  ACID.  Butyric  acid  is  found  in  rancid 
butter.  It  is  a  thick  liquid  with  a  disagreeable  odor. 

OLEIC  ACID,  C18H34O2,  stearic  acid,  C18H36O2,  and 
palmitic  acid,  C16H32O2,  occur  in  combination  with 
glycerin  to  form  most  of  the  natural  fats  and  oils. 
The  acids  are  white  solids  at  low  temperatures. 

ESTERS 

477.  Formation.  The  hydrogen  in  the  carboxyl 
of  an  organic  acid  may  be  replaced  by  an  alcohol 
radical,  just  as  inorganic  acids  and  bases  unite  in 
neutralization  (§  181);  the  products  are  water  and 
esters  or  ethereal  salts.  As  the  water  which  is  formed 
may  interfere  with  the  reaction,  concentrated  sul- 
furic acid  is  used  to  absorb  the  water.  Thus,  when 
a  mixture  of  ethyl  alcohol,  acetic  acid,  and  sulfuric 
acid  is  warmed,  ethyl  acetate  is  formed : 


Some  Common  Organic  Compounds  343 

C2HSOH  +  CH3C02H  -»  CH3C02C2H5  +  H2O 

(ethyl  acetate) 

The  analogy  between  this  reaction  and  the  reac- 
tion between  sodium  hydroxid  and  acetic  acid  is 
manifest: 

NaOH  +  CH3CO2H  —  >  NaCH3CO2  +  H2O 

(sodium  acetate} 

478.  Properties   of   Esters.      Many   esters    are 
found  in  fruits  and  flowers,  often  giving  to  them 
their  characteristic  flavor  and  fragrance.     Some  are 
prepared  by  artificial  means  and  used  as  cheap  sub- 
stitutes for  more  expensive  flavors  in  extracts,  per- 
fumery, and   beverages.     Thus,  ethyl  butyrate,  the 
ester  of  ethyl  alcchol  and  butyric  acid,  has  the  taste 
and  fragrance  of  pineapples,  amyl  acetate  that  of 
bananas,  and  amyl  valerate  that  of  apples. 

479.  Fats  and  Oils.     Most  animal  and  vegetable 
fats  and  oils,  such  as  suet,  tallow,  butter,  palm  and 
olive  oils,  consist   almost  entirely  of  mixtures  of 
glycerin    esters    or    ethers    of    oleic,-  stearic,   and 
palmitic  acids.    For  brevity  these  esters  are  termed 


%.i\&  palmitin,  C^.OCj  6H31O)3.  As  olein  is  liquid 
and  palmitin  and  stearin  solid  at  ordinary  tempera- 
tures, the  consistence  of  a  fat  or  oil  depends  on  rela- 
tive proportions  of  their  three  constituents. 

If  the  fats  or  oils  are  treated  with  sulfuric  acid 
or  heated  with  very  hot  steam,  they  break  up  into 
the  free  acids  and  glycerin;  if  they  are  boiled  with 
a  caustic  alkali  solution,  glycerin  is  freed,  and 
alkalin  salts  of  the  acids  are  formed.  The  fats  are 
said  to  be  saponified,  and  the  process  is  called  saponi- 
fication.  Thus,  if  stearin  be  boiled  with  sodium 


344  Elementary  Chemistry 

hydroxid  solution,  the  change  represented  by  the 
following  equation  takes  place: 
C3H5(OC18H350)3  +  3NaOH 

(stearin)        _>  3  C  t  8H3  5CO2Na  +  C3H5(OH)3 
(sodium  s  tear  ate)  (glycerin) 

480.  Soaps.  Soaps  consist  of  the  alkalin  salts 
of  palmitic,  stearic,  and  oleic  acids.  Hard  soaps 
contain  sodium  salts,  chiefly  of  the  solid  acids,  and 
soft  soaps  contain  potassium  salts,  principally  of 
oleic  acid.  The  kind  of  soap  also  varies  with  the 
fats  used.  Thus,  tallow,  lard,  palm  oil,,  and  cocoa- 
nut  oils  make  white  soap,  while  the  addition  of 
rosin,  cotton-seed  oil,  and  house  or  bone  grease, 
gives  the  soap  a  yellow  color.  Castile  soap  is  made 
from  olive  oil. 

MANUFACTURE  OF  SOAP.  By  means  of  steam  coils 
the  alkalin  solution  is  heated  in  an  immense  kettle  pro- 
vided with  stirrers,  and  the  fat  is  added.  The  mixture 
is  heated  to  boiling  until  the  saponification  is  complete. 
Salt  is  then  added,  whereupon  the  soap  separates  out  at 
the  top.  The  liquid  beneath  the  soap  is  drawn  off  and 
the  glycerin  which  it  contains  extracted.  The  soap  is 
then  washed  and  mixed  with  any  perfume  or  coloring 
matter  desired,  or  some  "filler,"  such  as  sodium  silicate, 
borax,  or  sand;  after  it  has  cooled  it  is  cut  into  bars, 
and  laid  out  to  dry. 

CARBOHYDRATES 

The  carbohydrates  form  a  numerous  group  of 
compounds,  the  most  important  members  of  which 
are  the  sugars  and  starch.  They  are  so  named 
because  they  contain  hydrogen  and  oxygen  in  the 
same  proportion  as  water,  and  were  for  that  reason 
formerly  considered  to  be  hydrates  of  carbon.  It 
is  now  known  that  such  is  not  the  case. 


Some  Common  Organic  Compounds  345 

481.  Sugars.     The  name  sugar  may  be  applied  to 
almost  any  sweet  substance  found  in  fruits,  vege- 
tables, or  the  sap  of  trees,  but  it  is  more  commonly 
used  to,  refer  to  the  sugar  which  is  derived  from 
sugar  cane  or  sugar  beets,  and  which  is  used  on  our 
tables  and  in  cooking.     Chemically  speaking,  how- 
ever, there  are  many  distinct  sugars  differing  in 
composition  from  these  two. 

482.  Cane  Sugar,  C12H22O11.-  Cane  sugar  (also 
called  sucrose  or  saccharose]  is  found  in  a  large  number 
of  plants,  but  our  supply  is  obtained  from  sugar  cane 
or  sugar  beets.     When  a  strong  sugar  solution  is 
allowed  to  flow  over  strings  hung  from  a  peg,  large 
transparent  crystals  are  formed,  which  are  .called 
rock  candy.     If  heated  to  about  160°,  sugar  melts,  and 
when  cool  forms  a  yellow  mass  known  as  barley 
sugar.     If  heated  to  about  200°,  it  is  changed  into 
caramel,  which  is  used  to  color  liquors  and  soups. 

MANUFACTURE  OF  CANE  SUGAR.  Sugar  cane  is 
crushed  between  rollers  and  the  juice  boiled  with  a 
little  lime;  the  scum  is  removed  from  time  to  time,  and 
the  solution  is  finally  filtered.  The  juice  thus  clarified 
is  evaporated  until  the  sugar  crystallizes  from  a  sample 
of  the  solution  when  it  is  cooled.  The  evaporation  is 
then  completed  in  pans  placed  in  a  vacuum,  as  there  is 
danger  of  discoloring  the  sugar  if  it  is  heated  too  high, 
and  because,  by  removing  the  pressure  of  the  air,  boil- 
ing takes  place  at  a  lower  temperature.  The  mass  of 
crystals  is  then  freed  from  the  adhering  liquor  by  whirl- 
ing in  a  centrifugal  machine.  The  solid  mass  which  is 
left  is  called  muscovado,  raiv,  or  brown  sugar,  while  the 
thick  liquid  is  molasses. 

Sugar  beets  are  reduced  to  a  pulp  or  cut  into  thin 
slices,  and  soaked  with  water  until  all  the  sugar  dif- 
fuses out  of  them.  The  solution  is  clarified  and  evap- 
orated, and  the  sugar  separated  in  much  the  same 


346  Elementary  Chemistry 

fashion  as  sugar  from  cane,  but  the  molasses  obtained  is 
not  fit  for  table  use. 

The  refining  of  sugar  obtained  from  both  of  the 
above  sources  consists  in  removing  the  impurities  and 
recrystallizing  the  sugar.  The  raw  sugar  is  dissolved 
in  water  contained  in  immense  tanks  and  the  solution 
heated.  It  is  stirred  by  blowing  air  into  it,  and  certain 
substances  are  added  to  gather  up  and  deposit  the 
impurities.  The  solution  is  then  filtered  through 
animal  charcoal,  which  removes  all  color  from  it.  The 
resulting  colorless  sirup  is  evaporated  in  vacuum  pans 
to  crystallization,  and  is  then  run  into  tanks  to  crystal- 
lize. The  crystals  are  separated  out  by  a  centrifugal 
machine,  and  the  liquid  boiled  over  again  or  made  into 
table  sirups.  The  crystalline  mass  is  so  dried  that  each 
grain  will  be  free,  and  we  have  the  familiar  granulated 
sugar. 

LACTOSE  OR  MILK  SUGAR.  Lactose  has  the  same 
composition  as  cane  sugar,  but  its  properties  are  differ- 
ent. It  is  obtained  from  milk,  and  forms  white,  gritty 
crystals,  which  are  not  so  sweet  as  cane  sugar.  It  is 
used  in  making  homeopathic  pills  and  infants'  foods. 

483.  Glucose,  C6H12O6.  Glucose,  dextrose  or 
grape  sugar,  is  found  in  many  sweet  fruits,  espe- 
cially grapes.  Raisins  (which  are  dried  grapes) 
are  often  coated  with  this  sugar.  Levulosc,  fructose 
or  fruit  sugar,  is  isomeric  with  glucose,  and  is 
often  found  associated  with  it,  as,  for  instance,  in 
honey.  When  cane  sugar  is  boiled  with  a  dilute 
acid,  it  takes  up  water,  and  both  dextrose  and 
levulose  are  formed : 

C,2H220,,  +  H20-»C6H12Ot  +  C«H1206 

(cane  sugar)  {dextrose)  {levulose) 

Both  these  sugars  are  fermentable,  and  yield  carbon 
dioxid  and  alcohol.  In  alkalin  solution  glucose  is 
a  powerful  reducing  agent.  When  sugar  is  boiled 
with  an  alkalin  solution  of  copper  sulfate,  called 


Some  Common  Organic  Compounds  347 

Fehling's    solution,   red   cuprous   oxid   is    formed. 
This  reaction  furnishes  a  test  for  sugar. 

"GLUCOSE."  The  ordinary  commercial  mixture 
called  "  glucose "  is  manufactured  by  boiling  starch 
with  dilute  sulfuric  acid.  The  liquid  products  which 
result  are  known  as  "  glucose  "  or  "  mixing  sirup,"  while 
the  solid  product  is  termed  "grape  sugar."  They  all 
contain  some  glucose  and  are  a  little  more  than  half  as 
sweet  as  cane  sugar.  But  as  they  are  cheaper  than 
cane  sugar,  they  are  used  extensively  in  its  place  in  the 
manufacture  of  the  poorer  grades  of  jelly,  candy,  and 
sirup. 

484.  Starch.     Starch  is  found  in  all  grains,  in 
most  vegetables,  and  in  parts  of  the  majority  of 
plants.     It  is   separated  by   mechanical   processes 
from  the  other  parts  of  plants.     As  usually  seen,  it 
forms  white  lumps  or  powder,  but  under  the  micro- 
scope it  is  seen  to  consist  of  oval  grains,  varying 
somewhat  in  appearance  with  the  source.     Starch 
is  almost  insoluble  in  cold  water,  but  if  it  be  treated 
with  boiling  water,  the  grains  swell  and  burst,  and 
form   a   solution   which    is    used   in   laundries    as 
"starch."     Immense  amounts  of  starch  are  used  in 
foods,  in  laundries,  in  finishing  paper  and  cloth, 
and  in  making  glucose. 

485.  Dextrin.     When    starch    is    treated    with 
dilute  acids  it  forms  a  sticky  solution,  from  which 
dextrin   is   prepared.     Mucilage   contains   a    large 
proportion  of  dextrin. 

BREAD.  Wheat  flour  is  about  three-fourths  starch 
and  about  one-eighth  water  and  one-eighth  gluten ; 
small  amounts  of  inorganic  salts  and  dextrin  are  also 
present.  In  making  bread,  a  little  yeast  is  mixed  with 
flour  and  water  (sometimes  also  milk)  and  the  resulting 
dough  thoroughly  kneaded.  When  the  dough  is  set  in 


348  Elementary  Chemistry 

a  warm  place  to  rise,  the  yeast  cells  multiply  and  con- 
vert the  fermentable  sugar  present  into  alcohol  and 
carbon  dioxid.  This  gas,  in  trying  to  escape,  puffs  up 
the  dough,  which  is  thereby  made  light  and  porous; 
the  bread  "rises."  When  the  bread  is  baked  the  high 
temperature  kills  the  yeast,  thus  stopping  the  fermenta- 
tion. '  The  alcohol,  carbon  dioxid,  and  more  or  less  of 
the  water  escape,  and  puff  up  the  dough  still  more. 
The  outside  of  the  bread  is  exposed  to  a  more  direct 
heat  than  the  interior  and  becomes  harder,  thus  forming 
the  crust.  Most  of  the  starch  undergoes  no  chemical 
change,  but  the  crust  is  largely  dextrin.  ;  ; 

486.  Cellulose,  (C6H10OS)«.  Cellulose  forms 
the  framework  of  most  vegetable  tissues,  and  is 
hence  very  abundant  and  widely  distributed. 
Wood,  cotton,  linen,  and  paper  are  made  up  largely 
of  cellulose.  When  pure,  cellulose  is  a  white  solid, 
insoluble  in  most  liquids.  Concentrated  sulfuric 
acid  will  dissolve  it  slowly,  and  if  the  solution  is 
diluted  and  boiled,  the  cellulose  is  converted  into  a 
mixture  of  dextrin  and  glucose.  Cellulose  behaves 
like  an  alcohol  in  that  it  reacts  with  acids  to  form 
esters. 

HIGH  EXPLOSIVES.  Cellulose  and  also  glycerin  react 
with  nitric  acid  to  form  highly  explosive  compounds. 
Nitroglycerin  is  a  yellow,  heavy  oil,  which,  when 
kindled,  burns  quietly,  but  if  subjected  to  a  sudden 
shock,  as  that  of  an  exploding  percussion  cap,  it 
explodes  with  great  violence. 

Dynamite  consists  of  some  fine  powder,  as  infusorial 
earth  or  wood  pulp,  soaked  with  nitroglycerin.  Gun 
cotton  is  cellulose  nitrate,  and  looks  very  similar  to 
ordinary  cotton.  It  burns  rapidly  but  quietly  when 
ignited,  but  explodes  when  a  percussion  cap  is  set  off 
in  it.  Collodion  is  a  solution  of  gun  cotton  in  a  mixture 
of  alcohol  and  ether.  When  collodion  is  spread  upon  a 
glass  plate  or  the  skin,  the  solvent  soon  evaporates  and 
leaves  a  thin  film  of  gun  cotton.  ;This  film  protects 


Some  Common  Organic  Compounds  349 

wounds  from  the  action  of  the  air,  and  it  is  also  utilized 
in  the  preparation  of  "  wet  process"  photographic  plates. 

Celluloid  consists  of  a  mixture  of  gun  cotton  and 
camphor.  It  is  readily  molded  and  is  put  to  a  variety 
of  uses.  It  smells  of  camphor,  is  readily  set  on  fire,  and 
burns  freely  with  a  smoky  flame. 

PAPER.  Paper  is  more  or  less  pure  cellulose  mixed 
with" various  other,  ingredients,  added  ^f or  the  purpose  of 
imparting  a  special  surface  or  color.  The  best  paper  is 
made  from  rags,  .but  that  used  in  newspapers  and  many 
books  is  made  from  wood. 

In  making  paper,  the  rags  or  wood  are  first  reduced 
to  a  pulp,  which  is  spread  on  a  wire  gauze,  dried,  and 
pressed.  Wood  pulp  is  commonly  made  by  heating 
under  pressure  chips  of  wrood  (spruce  is  best)  with  a 
solution  of  caustic  soda,  or  of  sodium  (calcium)  bisul- 
fite. The  pulp  is  usually  mixed  with  clay,  gypsum, 
aluminum  sulfate,  or  other  substances,  so  as  to  make  it 
of  closer  texture  and  more  opaque.  The  paper  is  then 
said  to  be  "filled."  The  paper  on  which  this  "book  is 
printed  is  filled  with  clay.  Paper  that  is  to  be  used  for 
printing  or  writing  is  covered  with  a  "  size  "  consisting 
of  gelatin,  rosin,  or  other  substance  which  will  keep 
the  ink  from  spreading.  Most  paper  is  finished  by 
passing  it  between  heavy  rollers. 

BENZENE  DERIVATIVES 

487.  Coal  Tar.     In  the  manufacture  of  illumin- 
ating gas  (page  9-1)  there  collects  in  the  hydraulic 
main  and  condensers  a  thick,  black,  bad-smelling 
liquid,  which  is  called  coal  tar.     Some  of  this  is  used 
in  preserving  timber  and  in  making  tarred  paper 
and  paint,  but  most  of  it  is  distilled,  whereby  it  is 
separated  into  various  constituents. 

488.  Benzene,  C6H6.     Benzene  is  a  light,  color- 
less liquid,  not  miscible  with  water ;  it  gives  off  an 
odor  something  like  that  of  illuminating  gas.     Ben- 
zene dissolves  fats,  resins,  iodin,  sulfur,  and  rubber. 


350  Elementary  Chemistry 

Its  main  use  is  in  the  preparation  of  its  deriva- 
tives, which  are  numerous  and  important. 

NOTE.  Benzene  is  sometimes  called  benzol,  and  should  not  be 
confused  with  benzine,  which  is  one  of  the  products  of  the  distilla- 
tion of  petroleum. 

CONSTITUTION  OF  THE  BENZENE  MOLECULE.  It  is 
believed  that  the  atoms  of  carbon  in  the  benzene  mole- 
cule are  arranged  in  a  ring,  and  that  every  other  carbon 
atom  is  combined  with  its  neighbor  by  a  double  bond. 
The  structural  formula  is  usually  written  : 

H 

i 

//CN 

H-C          C-H 

I  I! 

H-C          C-H 


H 

In  all  of  the  numerous  compounds  of  benzene  this 
ring-shaped  structure  remains  intact.  Not  one  of  the 
atoms  of  carbon  may  be  taken  away  without  causing 
complete  decomposition.  The  derivatives  are  formed 
by  the  substitution  of  other  elements  or  radicals  for  the 
hydrogen. 

489.  Toluene,  C7H8.  Toluene,  which  much 
resembles  benzene,  may  be  regarded  as  methyl 
benzene,  C6H5CH3,  where  one  hydrogen  atom  is 
replaced  by  the  radical,  methyl,  CH3,  or  as  phenyl 
methane,  where  one  of  the  hydrogen  atoms  of 
methane,  CH4,  may  be  considered  to  be  replaced  by 
the  radical,  phenyl,  C  6  H  - . 

490.  Phenol,  C6H5OH.  Phenol  is  a  white,  crys- 
talline solid,  with  a  smoky  odor  and  sharp  taste.  It 
is  corrosive  and  poisonous.  Its  solution  in  water  is 


Some  Common  Organic  Compounds  351 

called  carbolic  acid  and  is  used  as  a  disinfectant. 
Picric  acid,  or  tri-nitro-phenol,  C6H2(NO2)3OH,  a 
derivative  of  phenol,  forms  yellow  crystals  soluble 
in  water.  It  is  used  in  dyeing  silk  yellow  and  in 
the  manufacture  of  high  explosives. 

491.  Nitrobenzene,  C6HSNO2.     Nitrobenzene  is 
the  yellow  liquid  obtained  from  the  action  of  nitric 
acid  on  benzene.     It  has  the  odor  of  bitter  almonds, 
and,  although  poisonous,  is  frequently  used  in  pro- 
ducing the  flavor  of  bitter  almonds. 

492.  Anilin,  C6HSNH2.    Anilin  is  a  colorless  oil 
prepared  by  the  reduction  of  nitrobenzene.     Many 
compounds  known  as  anilin  dyes  are  derived  from  it. 

493.  Benzoic  Acid,  C6HSCO2H.      Benzoic  acid 
is  found  in  certain  gums,  and  is  usually  prepared 
from  gum  benzoin.     It  forms  small  white  crystals 
with  a  pleasant  odor. 

494.  Benzoic    Aldehyde,    C6HSCOH.      Benzoic 
aldehyde,  commonly  known  as  oil  of  bitter  almonds, 
is  used  as  a  flavoring  substance. 

495.  Salicylic  Acid,   C6H4OHCO2H.     Salicylic 
acid  forms  white  crystals  and  is  used  as  a  food  pre- 
servative.     Sodium  salicylate  is  a  specific  remedy  for 
rheumatism,  and  methyl  salicylate  is  the  compound 
which  gives  the  flavor  to  wintergreen. 

496.  Naphthalene,  C ,  0  H  8 .    Naphthalene  also  is 
obtained   from   coal   tar.     It   forms  white  crystals 
which  have  a  disagreeable  odor,  and  are  in  common 
use  as  "  moth  balls." 

497.  Glucosides.      Glucosides    occur    in    many 
plants  and  by  the  action  of  ferments  are  converted 
into  glucose,  benzene  derivatives,  and  other  com- 
pounds.    Thus,  amygdalin  is  found  in  laurel  leaves, 


352  Elementary  Chemistry 

bitter  almonds,  and  cherry  and  peach  kernels.  The 
ferment  emulsin,  which  also  occurs  in  plants,  causes 
the  amygdalin  to  break  up  into  benzoic  aldehyde, 
glucose,  and  hydrocyanic  acid. 

The  class  of  compounds  known  as  tannins  are  also 
glucosides.  They  occur  in  the  leaves  and  bark  of 
the  oak,  hemlock,  and  pine,  as  well  as  in  tea,  coffee, 
sumach,  gall  nuts,  and  numerous  plants.  Gallic  and 
tannic  acids  are  the  best  known  derivatives  of  the 
tannins ;  tannic  acid  is  often  called  simply  tannin. 
Iron  salts  produce  black  compounds  with  tannin, 
and  its  presence  may  be  shown  in  decoctions  of  tea, 
hemlock  bark,  or  oak  bark,  by  the  appearance  of  a 
black  precipitate  when  ferrous  sulfate  is  added. 
The  best  writing  ink  is  made  from  iron  compounds 
and  tannin.  When  fresh  hides  are  soaked  in  'solu- 
tions of  tannin,  reactions  take  place  which  convert 
the  hides  into  leather ;  the  hides  are  tanned. 

498.  Alkaloids.  Alkaloids  are  extracted  from 
plants,  and  are  characterized  by  the  physiological 
effect  they  have  upon  animals.  They  all  contain 
nitrogen,  and  act  like  ammonia  in  having  an  alkalin 
reaction  and"  in  combining  directly  with  acids  to 
form  salts.  Many  of  these  salts  are  used  as  medi- 
cines. 

Opium  is  the  dried  sap  of  unripe  poppies  ;  it  contains 
several  alkaloids,  chief  of  which  is  morpliinc,  used  to 
alleviate  pain  and  induce  sleep.  Laudanum  and  pare- 
goric are  preparations  of  opium.  Quinine  is  extracted 
from  the  bark  of  the  cinchona  tree,  and  is  used  as  a 
remedy  in  fevers.  Cocaine,  obtained  from  the  coca 
|>lant,  is  used  largely  in  dentistry  and  minor  surgery  as 
a;  local  anaesthetic.  Nicotine  occurs  in"  tobacco,  and 
ffieinv  or  caffeine  in  tea  and  coffee. 


APPENDIXES 


APPENDIX  A 


QUALITATIVE  ANALYSIS 


INTRODUCTORY 

Qualitative  chemical  analysis  has  to  do  with  the  operations  and 
methods  which  are  employed  in  finding  out  what  elements  and 
radicals  are  contained  in  a  substance  or  mixture  of  substances. 

Qualitative  analysis  consists  mainly  of  the  study  of  the  solu- 
bilities of  substances.  In  the  usual  scheme  of  analysis  the  sub- 
stance to  be  analyzed  is  first  brought  into  solution.  A  solution  of 
a  known  compound  (a  reagent)  is  then  added  to  this  solution,  and 
if  a  precipitate  of  certain  properties  is  formed,  a  definite  conclusion 
may  be  drawn  as  to  the  presence  of  certain  elements  or  radicals 
in  the  original  substance  taken.  Other  known  solutions  are  added 
to  the  filtrate  from  this  precipitate,  and  from  the  formation  of 
additional  precipitates  and  observation  of  their  properties  further 
conclusions  can  be  drawn  as  to  the  composition  of  the  original 
substance 

The  solubilities  of  certain  salts  of  the  commoner  metals  permit 
of  their  classification  into  five  groups,  which  are  usually  given  the 
name  of  the  reagent  which  is  added  to  effect  the  precipitation. 
These  groups  are: 

f         Lead 

I.  Hydrochloric  Mercury 

Acid  Group  (p  us  salts) 

Silver 


Precipitated  as  chlorids, 
PbCl2,  HgCl,  AgCl,  by  hy- 
drochloric acid. 


Lead 


Mercury 

(ic  salts) 

. 

II.  Hydrogen 
Sulfid  Group 

Copper 
Cadmium 
Bismuth 

Tin 

Antimony 

•Arsenic 

Precipitated  as  sulfids,  PbS, 
HgS,  CuS,  CdS,  Bi,S8,SnS  or 


SnS2,  Sb2S3,  or 


,  As3S3 


or  AsaS5,  by  hydrogen  sulfid. 
The  last  three  are  soluble  in 
yellow  ammonium  sulfid,  the 
others  not. 


n, 


[i] 


11 


Elementary  Chemistry 


III.  Ammonium 
Sulfid  Grotm 


Aluminum 

Chromium 

Iron 

Cobalt 

Nickel 

Manganese 

Zinc 


The  first  three  are  precipi- 
tated as  hydroxids,  A1(OH)3, 
Cr(OH)3,  Fe(OH)3,  by  am- 
monium hydroxid.  The  last 
four  are  precipitated  as  sul- 
fids,  CoS,  NiS,  MnS,  ZnS,  by 
ammonium  sulfid. 


IV.  Ammonium 
Carbonate 
Group 


Calcium 
Strontium 

Barium 
Magnesium 


Precipitated    as    carbonates, 

CaCO3,  SrCO3,  BaCO3, 
MgCO3  (soluble  in  NH4C1), 
by  ammonium  carbonate. 


V.  Alkali  Metals 


Lithium 
Sodium 
Potassium 
I  Ammonium 


Not  precipitated  by  any  com- 
mon reagents. 


I.     HYDROCHLORIC   ACID   GROUP 

METHOD  OF  ANALYSIS 

Add  HC1  a  little  at  a  time  to  the  solution  as  long  as  a  precipi- 
tate (ptt.)  is  formed.  Shake  up  well,  filter,  and  wash  twice  with  a 
little  cold  water.  Punch  a  hole  in  the  apex  of  the  filter  paper  and 
wash  the  precipitate  into  a  beaker.  Boil  the  water  and  filter 
while  hot. 


Residue :  AgCl,  HgCl. 

Wash  with   hot  water  and 
twice  pour  over  it  enough 


Filtrate:  PbCl2 
Divide  into  two  portions. 
PORTION  I.     Add  K,Cr2O7  or 


i\  n4vjn  to  cover  it. 

K2CrO4  ;   a  yellow  ptt.  soluble 
in  NaOH   indicates    the    pres- 
ence of  lead. 
PORTION  II.     Add  KI  ;   a  yel- 
low ptt.   soluble  in  hot  water 
and    recrystallizing    in    plates 
on  cooling  proves  the  presence 
of  lead. 

Residue: 
Hg-NH2-Cl 
and  Hg. 

A  black  resi- 
.due  proves  the 
presence  otmer- 
cury. 

Filtrate  : 
AgCl'2NH3 

Acidifv  with 
HNO3;  a  white 
ptt.  proves  the 
presence   of 
silver. 

Qualitative  Analysis  iii 

REACTIONS  OF  SOLUTIONS  OF  SILVER,  LEAD,  AND 
MERCUROUS  SALTS 


SILVER 

HC1  precipitates  AgCl,  white,  curdy,  changing  on  exposure  to 
the  light  from  lavender  to  black  ;  soluble  in  NH4OH,  forming 
AgCl  •  2NH3,  from  which  solution  HNO3  reprecipitates  AgCl. 

LEAD 

HC1  precipitates  PbCl2,  white,  flocculent,  soluble  in  hot  water, 
crystallizing  in  long  needles  when  solution  cools. 

H2SO4  precipitates  PbSO4,  white. 

K.,Cr2O7  or  K2CrO4  precipitates  PbCrO4,  yellow,  soluble  in 
NaOH. 

KI  precipitates  PbI2,  yellow,  soluble  in  hot  water,  from  which 
when  cold  it  crystallizes  in  shining  plates. 

H,S  precipitates  PbS,  black,  changed  by  hot  and  moderately 
concentrated  HNO3  into  sulfur  and  Pb(NO3)2,  which  is  soluble. 

MERCURY 

HC1  precipitates  HgCl,  white,  changed  by  NH4OH  into  a 
black  mixture  of  HgNH,Cl  and  Hg. 


II.     HYDROGEN   SULFID   GROUP 
METHOD  OF  ANALYSIS 

Warm  the  filtrate  from  the  Hydrochloric  Acid  Group  and  pass 
a  current  of  hydrogen  sulfid  through  it.  Make  sure  that  precipi- 
tation is  complete  by  filtering  a  small  portion,  diluting  the 
filtrate,  and  treating  it  with  H2S  a  few  minutes.  Filter  and  wash 
thoroughly  with  hot  water.  Put  a  small  portion  of  the  precipitate 
in  an  evaporating  dish  ;  add  a  little  ammonium  polysulfid.  If  this 
precipitate  dissolves  completely,  Division  A  is  absent ;  if  not, 
treat  the  remainder  of  the  precipitate  with  ammonium  polysulfid 
and  warm  (not  boil}  for  about  three  minutes  with  occasional 
stirring.  Filter  while  hot  and  proceed  as  indicated  in  table  for 
Division  A. 


IV 


Elementary  Chemistry 


DIVISION  A 

Boil  the  precipitate  in  an  evaporating  dish  with  a  small  amount 
of  a  mixture  of  equal  volumes  of  strong  nitric  acid  and  water 
until  brown  fumes  cease  to  be  given  off  freely.  Dilute  with  a 
little  water  and  filter. 


Filtrate  :  Lead,  Bismuth,  Copper,  Cadmium  Salts. 

Add  a  little  strong  H2SO4  and  evaporate  with 
care  until  dense  white  fumes  appear.    Add  an  equal 


volume  of  dilute  H255O4  and  niter. 

Boil  with 

a  very  little 

Filtrate  : 

Residue: 

aqua  regia. 

Bismuth,  Copper,  Cadmium  Salts. 

PbS04 

Filter,   boil 
the  filtrate 

Add  NH4OH  until  strongly  alkalin. 

Wash, 

until    chlo- 

A  deep  blue  solution  proves  the  pres- 

warm  the 

rin  is  ex- 

ence of  copper.     A  white  ptt.  indicates 

ptt.    with 

pelled,  then 

bismuth.     Filter  and  wash. 

ammonium 

add   SnCl2 

acetate 

and    warm. 

Fil 

Copper,  Ca 
If  copper  is 
absent  : 

trate  : 

dmium  Salts. 
If  -copper   is 
present: 

Precipitate 
Bi  (OH)8  or 
basic    salt 
of  bismuth. 

and  a  few 
drops  of 
HC2H302 
and  filter. 
To  the  fil- 

A gray  or 
black    "ptt. 
proves  the 
presence  of 
mercury. 

Make  slight- 
Iv  acid  with 

Acidify  with 
dil.  HC1  and 

Add    two 
or    three 

trate   add 
K2CrO4   or 

dil.  HC1  and 

treat  with 

precipitate 
with     H2S. 

drops   of 
HC1  to  the 

K2Cr2O7. 
A    yellow 

H2S. 

Filter    and 

ptt.  in  the 

ptt.  soluble 

A    yellow 

boil   the    ptt. 

funnel   and 

in    NaOH 

ptt.  proves 

immediately 

allow    the 

proves   the 

the    pres- 

with dilute 

nitrate    to 

presence  of 

ence  of  cad- 

H2SO4.    Fil- 

drop into  a 

lead. 

mium. 

ter,  rejecting 

beaker    of 

the    residue. 

water. 

Dilute    the 

A  white 

colorless    fil- 

ptt. proves 

trate  with  an 

the    pres- 

equal volume 

ence  of  bis- 

of water  and 

muth. 

treat    with 

H2S. 

A    yellow 

ptt.   proves 

the    presence 

of   cadmium. 

Residue: 

Mercuric 
Salt. 


Qualitative  Analysis  v 

REACTIONS  OF  SOLUTIONS  OF  MERCURIC,  CUPRIC, 
CADMIUM,  AND  BISMUTH  SALTS 

MERCURY 

II 2S  precipitates  HgS,  black,  insoluble  in  hot  and  concentrated 
HNO3,  but  changed  by  prolonged  action  of  that  reagent  into 
Hg(NO3)2-  2  HgS,  white  and  insoluble  in  concentrated  HNO3. 
Both  Hg(NO3)2"  2  HgS  and  HgS  are  changed  by  aqua  regia  into 
sulfur  and  HgCl2,  which  is  soluble.  HgS  is  insoluble  in  (NH4)2S. 

SnCl2  reduces  HgCl2  to  HgCl,  white.  An  excess  of  SnCl2 
reduces  the  HgCl  more  or  less  to  mercury,  which  gives  the  HgCl 
a  darker  color. 

COPPER 

H2S  precipitates  CuS,  black,  changed  by  hot  and  concentrated 
HNO3  into  sulfur  and  Cu(NO3)2,  which  is  soluble.  CuS  is  insol- 
uble in  dilute  H,SO4.  CuS  is  slightly  soluble  in  (NH4)2S. 

NH4OH  precipitates  light  blue  basic  salts,  readily  soluble  in 
excess,  producing  deep  blue  solutions  of  ammonia  cupric  salts,  as 


CADMIUM 

H2S  precipitates  CdS,  varying  in  color  from  light  yellow  to 
orange  according  to  the  conditions  under  which  precipitation 
takes  place ;  easily  soluble  in  concentrated  HC1  or  in  hot  and 
dilute  H2SO4  ;  change:!  by  hot  and  concentrated  HNO3  into 
sulfur  and  Cd(NO3)2,  which  is  soluble.  CdS  is  insoluble  in 
(NH4),S. 

NH4OH  precipitates  Cd(OH)2,  white,  readily  soluble  in  excess, 
producing  ammonia  cadmium  salts,  as  Cd(NO3)2'  4NH3. 

BISMUTH 

H2S  precipitates  Bi2S3,  dark  brown  ;  changed  by  hot  and  con- 
centrated HNO3  into  sulfur  and  Bi(NO3)3,  which  is  soluble.  Bi2S3 
is  insoluble  in  (NH4)2S. 

H.tO  added  in  large  proportion  to  solutions  of  bismuth  salts 
which  do  not  contain  too  much  acid,  precipitates  basic  salts,  as 
BiOCl,  (BiO)2SO4,  BiONO3,  etc. 

NH4OH  precipitates  Bi(OH)3  or  a  basic  salt,  white  ;  insoluble 
in  excess  ;  soluble  in  dilute  HC1. 


VI 


Elementary  Chemistry 


DIVISION  B 

Slightly  acidify  the  ammonium  sulfid  solution  with  HC1.  [If 
the  precipitate  is  white  it  is  probably  only  sulfur.]  Filter,  reject- 
ing the  filtrate,  as  it  contains  no  metals,  transfer  the  precipitate 
to  a  beaker,  add  a  little  concentrated  HC1,  heat  to  boiling  for  a 
few  minutes,  and  filter. 


Filtrate :     Tin,  Antimony  salts. 
Place  a  bright  iron  wire  or  nail  in  the 
filtrate,  warm  gently,  let  stand  for  fifteen 
minutes,  and  then  filter. 


Filtrate : 

SnCl2 

Add  HgCl2. 
A  white  ptt.  get- 
ting gray  when 
more  of  HgCl2 
is  added  and 
heat  applied, 
proves  presence 
of  tin. 


Precipitate:    Antimony 
(in  metallic  state). 

Wash  thoroughly  and 
transfer  to  a  beaker.  Dis- 
solve in  a  little  cone,  HC1 
to  which  a  few  drops  of 
cone.  HNO3  has  been 
added.  Evaporate  nearly 
to  dryness;  then  add  a 
large  proportion  of  water. 
The  formation  of  a  white 
ptt.  proves  the  presence  of 
antimony. 

[Proof  may  be  confirmed 
by  passing  H2S  into  solu- 
tion with  formation  of 
orange  ptt.] 


Residue: 

Arsenic  Sulfids. 

Dissolve  in  hot, 
cone.  HNO3.  Add 
a  little  of  the  solu- 
tion to  a  test  tube 
nearly  half  full  of  a 
solution  of  ammo- 
nium molybdate, 
and  warm  gently. 

A  yellow  crystal- 
line ptt.  proves  the 
presence  of  arsenic. 
Also  try  the  special 
tests. 


REACTIONS  OF  SOLUTIONS  OF  TIN,  ANTIMONY,  AND 
ARSENIC  SALTS 

TIN  (Stannous) 

H2S  precipitates  SnS,  dark  brown ;  soluble  in  warm  concen- 
trated HC1 ;  soluble  in  (NH4)2S,  forming  sulfo-stannates,  as 
(NH4)2SnS3,  from  which  a  dilute  acid  precipitates  SnS2,  yellow. 

HgCl2  is  reduced  by  SnCl2  in  HC1  solution  to  HgCl,  white; 
an  excess  of  SnCl2  reduces  some  of  the  HgCl  to  mercury,  which 
imparts  a  darker  color  to  the  precipitate. 

TIN  (Stannic} 

H2S  precipitates  SnS2,  yellow,  from  solutions  not  containing 
too  much  HC1 ;  soluble  in  warm  concentrated  HC1 ;  soluble  in 
(NH4)2S,  forming  sulfo-stannates,  as  (NH4)2SnS3. 


Qualitative  Analysis  vii 

ANTIMONY  (ous) 

H2S  precipitates  Sb2S3,  orange  red  ;  soluble  in  warm,  concen- 
trated HC1 ;  oxidized  by  hot,  concentrated  HNO3,  forming  sulfur 
and  H3SbO4,  which  is  soluble.  Sb2S3  is  soluble  in  (NH4)2S, 
forming  sulfo-antimonates,  as  (NH4)3SbS4,  from  which  dilute 
acids  precipitate  Sb2S5,  orange  red. 

When  SbCl3  is  added  to  a  large  proportion  of  water,  SbOCl, 
white,  is  produced,  which  is  changed  directly  to  Sb2S3  when 
treated  with  H,S. 

ANTIMONY  (ic) 

H2S  precipitates  Sb2S5,  orange  red,  and  resembling  Sb2S3 
in  its  behavior  toward  most  reagents. 

ARSENIC  (ous) 

H2S  precipitates  As2S3,  lemon  yellow;  almost  insoluble  in 
warm,  concentrated  HC1 ;  oxidized  by  hot  concentrated  HNO3 
to  H3AsO4,  which  is  soluble,  sulfur  being  set  free.  As2S3  is 
soluble  in  (NH4)2S,  forming  sulfo-arsenates,  as  (NH4)3AsS4,  from 
which  HC1  precipitates  As2S5. 

ARSENIC  (ic) 

H2S  precipitates  As2Ss,  lemon  yellow,  and  resembling  As,S3 
in  its  behavior  toward  most  reagents.  The  precipitation  takes 
place  slowly  and  is  more  complete  if  the  solution  is  warm,  when 
H2S  reduces  the  arsenic  solution  to  the  arsenious  condition  and 
As2S3  is  precipitated. 

(NH4)2MoO4,  ammonium  molybdate,  added  in  excess  to  a 
solution  of  arsenic  acid  containing  HNO3  precipitates  ammonium 
arseno-molybdate,  yellow.  Precipitation  is  best  obtained  by 
adding  the  arsenic  solution  to  a  small  test  tube  half  full  of 
(NH4)2MoO4.  The  mixture  should  then  be  warmed,  but  should 
not  be  heated  above  70°,  lest  MoO3,  white,  be  precipitated. 

III.     AMMONIUM   SULFID   GROUP 

METHOD  OF  ANALYSIS 

Add  NH4OH  to  slight  alkalinity,  heat  to  boiling,  then  add 
(NH4)2S  in  slight  excess;  heat  again  to  boiling  and  allow  the 
precipitate  to  settle.  Filter  and  wash  thoroughly  with  hot 
water.  Without  delay  treat  the  precipitate  in  an  evaporating 
dish  with  a  mixture  of  equal  volumes  of  strong  HC1  and  water, 
stirring  well.  Filter  and  wash  immediately. 


VI 11 


Elementary  Chemistry 


Residue: 

Nickel,    Cobalt    Sulr 


Filtrate:  Iron,  Aluminum,  Chromium,  Zinc, 
Manganese  Chlorids. 


rids. 
Test   with   borax 

Expel  any  H2S  which  may  be  present  by 
boiling  and  divide  into  two  unequal  portions. 

bead  ;    blue,   cobalt  ; 

PORTION  I.    Evaporate  the  smaller  portion 

brown,  nickel. 

to  small  bulk,  add  a  little  chlorin  water, 

To  detect   one   of 

and  boil  until  excess  of  chlorin  is  expelled. 

these  metals  in  the 

To  the  cooled  solution  add  KCNS.     A  red 

presence  of  the  other, 

color  proves  the  presence  of  iron. 

dissolve  the  residue 

PORTION  II.     To  the  larger  portion  add 

in  a  little  aqua  regia. 
Filter  and  evaporate 
to  small  bulk.     Heat 
to  boiling   and   add 

a  little  cone.  HNO3  and  boil.      Evaporate 
to   small  bulk.     Nearly  neutralize  with 
(NH4)2CO3,  and,  transferring  the  solution 
to  a  flask,  add  five  times  its  volume  of  sus- 

an equal  bulk  of  bro- 
min  water  and  then 

pended  BaCO3.     Shake  the  flask  vigorously 
from  time  to  time  for  half  an  hour  and  then 

of  NaOH.     Boil  vig- 

filter. 

orously   and    add    a 

little    bromin    water 

from   time   to   time. 

Precipitate  : 

Filtrate:     Zinc, 

Wash  thoroughly 

Chromium,  Aluminum, 

Manganese  Salts. 

with    boiling    water 

Iron  Hydroxids. 

PORTION  I.      Add 

bydecantation,  filter 
and  boil  the  ptt.  with 
NH4OH  and  NH4Cl 

A     fi"\4- 

PORTION  I.     Fuse   on 
platinum  foil  with 
Na2C03andKN03.    A 

HC2H302     and 
then    H2S.      A 
white  ptt.    soluble 

and  niter. 

yellow  product  indicates 

in  HC1  proves  the 

the   presence   of   chro- 

presence of  zinc. 

Residue: 

Filtrate: 

mium.     Dissolve  in 

PORTION  II.      Put 

Cobalt 

Nickel. 

water  and  make    acid 

a  very  little  in  an 

[Co(OH)3] 

Test  with 
borax 
bead. 

Treat 
withH2S 
A  black 
ptt.  indi- 

withHC2H3O2.   A  red 
ptt.  with  AgNO3   and 
a  yellow  ptt.    with 
Pb(C2H3O2)2   proves 
the  presence   of  chro- 

evaporating    dish, 
add  1  cubic  centi- 
meter   of    cone. 
H2SO4    and    heat 
until   dense    white 

cates  the 

miiim. 

fumes    appear. 

presence 
of  nickel  . 

PORTION  II.     Add  an 

Transfer  the  cooled 

equal    bulk    of    solid 

contents    of    the 

v^onnrm 

Na2CO3,  half  as  much 

dish  to  a  test  tube 

\vitn    DO- 
TO  -V"   VlAQ  f\ 

Ba(OH),,  and  5  cubic 

half  full  of  H2SO4) 

I  ctX  UtJdU.. 

centimeters    of    water. 

add  PbO2,  heat  to 

Boil  two  or  three  min- 

boiling  and   allow 

utes.    Filter,  and  to  the 

to  stand  until  sus- 

filtrate add  NH4C1  and 

pended  matter  set- 

boil for  some  time.     A 

tles.      A   red    or 

white    ptt.  ,    best    seen 

purple   colored  so- 

against   a    dark   back- 

lution   proves    the 

ground,  proves  the 

presence    of  man- 

presence of  aliimimirn. 

ganese. 

Qualitative  Analysis  ix 

REACTIONS  OF  SOLUTIONS  OF  NICKEL,  COBALT,  IRON, 

MANGANESE,  ZINC,  ALUMINUM,  AND 

CHROMIUM  SALTS 

NICKEL 

NH4OH  in  small  proportion  precipitates  Ni(OH)2,  green  ;  if 
in  excess,  greenish  blue  basic'salts.  The  precipitates  are  soluble 
in  NH4OH  in  the  presence  of  ammonium  salts.  Both  solutions 
and  precipitates  are  changed  by  (NH4)2S  into  NiS,  black. 

KOH  or  NaOH  precipitates  Ni(OH)2,  green  ;  insoluble  in 
excess.  Ni(OH)2  is  oxidized  by  boiling  with  bromin  water  and 
NaOH  to  Ni(OH)3,  black  ;  when  this  is  boiled  with  NH4OH  and 
NH4C1  it  dissolves. 

(NH4)2S  precipitates  from  neutral  or  alkalin  solutions  NiS, 
black ;  somewhat  soluble  in  excess  of  (NH4)2S,  more  readily  in 
the  presence  of  NH4OH,  forming  a  dark  brown  solution  from 
which  NiS  is  reprecipitated  if  the  solvent  is  removed  by  boiling. 
NiS  is  insoluble  in  cold  and  not  very  dilute  HC1 ;  it  is  changed 
by  aqua  regia  to  free  sulfur  and  NiCl2,  which  dissolves.  NiS  is 
oxidized  by  the  oxygen  of  the  air  to  NiSO4. 

A  borax  bead  is  colored  brown  when  fused  with  a  compound 
of  nickel. 

COBALT 

NH4OH  precipitates  blue  basic  salts  ;  easily  soluble  in  NH4OH 
in  the  presence  of  ammonium  salts.  Both  precipitate  and  solution 
are  changed  by  (NHt)2S  into  CoS. 

KOH  or  NaOH  precipitates  from  cold  solutions  a  blue  basic 
salt  which,  when  warmed  with  the  alkali,  changes  to  Co(OH)2, 
pink.  Co(OH)2  is  oxidized  to  Co(OH)3,  black,  by  boiling  with 
bromin  water  and  NaOH.  The  Co(OH)3  is  not  affected  by  boil- 
ing with  NH4OH  and  NH4C1. 

(NH4)2S  precipitates  from  neutral  or  alkalin  solutions  CoS, 
black  ;  insoluble  in  excess  ;  practically  insoluble  in  not  very  dilute 
HC1 ;  attacked  by  aqua  regia,  forming  sulfur  and  CoCl2,  which 
dissolves.  CoS  is  oxidized  by  the  air  to  CoSO4. 

A  borax  bead  is  colored  blue  when  fused  with  a  compound  of 
cobalt. 

IRON  (Ferrous) 

NOTE.  As  ferrous  salts  oxidize  very  readily  to  ferric,  it  is  only 
by  taking  special  precautions  that  a  solution  of  ferrous  salt  can 


x  Elementary  Chemistry 

be  kept  from  oxidizing.  The  solution  of  FeSO4  should  be  heated 
with  iron  filings  and  H2SO4,  when  the  hydrogen  will  reduce  any 
ferric  salt  to  the  ferrous  condition. 

NH4OH  in  neutral  solutions  precipitates  incompletely 
Fe(OH)2,  which  oxidizes  promptly  to  compounds  first  green,  then 
black,  and  finally  reddish  brown  Fe(OH>3.  When  these  precip- 
itates are  treated  with  H2S  they  change  into  FeS,  black. 

KOH  or  NaOH  precipitates  Fe(OH)2,  white,  but  oxidizing  as 
described  above. 

(NH4)2S  precipitates  FeS,  black  ;  attacked  by  hot  concentrated 
HNO3,  forming  sulfur  and  Fe(NO3)3,  which  dissolves.  FeS  is 
soluble  in  dilute  HC1,  and  on  exposure  to  moist  air  oxidizes  to 
FeSO4,  and  finally  to  a  basic  ferric  sulfate  which  is  brown. 

BaCO3,  shaken  with  a  cold,  neutral,  or  slightly  acid  solution  of 
FeCl2,  does  not  precipitate  a  compound  of  iron.  It  is  most  con- 
venient to  employ  the  BaCO3  suspended  in  water. 

KCNS,  potassium  sulfocyanate,  produces  no  red  coloration  in 
solutions  of  ferrous  salts. 

Concentrated  HNO3,  or  chlorin  water,  oxidizes  ferrous  to  ferric 
salts  very  promptly  at  the  boiling  temperature. 

IRON  (Ferric} 

NH4OH,  KOH,  or  NaOH,  precipitates  Fe(OH)3,  reddish  brown 
and  gelatinous  ;  changed  by  (NH4)2S  into  FeS,  black. 

BaCO3,  when  shaken  with  a  cold,  neutral,  or  but  slightly  acid 
solution  of  a  ferric  salt,  precipitates  Fe(OH)3  or  a  basic  salt. 

KCNS,  potassium  sulfocyanate,  in  excess,  forms  with  solutions 
of  ferric  salts  a  deep  red  complex  soluble  salt. 

H2S  reduces  acid  solutions  of  ferric  salts  to  the  ferrous  condi- 
tion with  separation  of  sulfur. 

MANGANESE  (ous) 

NH4OH,  KOH,  or  NaOH,  precipitates  Mn(OH)2,  white,  oxi- 
dized quickly  to  dark  brown  compounds.  The  precipitate  is 
changed  to  MnS  by  (NH4),S. 

(NH4)2S  precipitates  MnS,  pink,  soluble  in  dilute  acids  ;  when 
exposed  to  the  air  it  turns  brown. 

BaCO3,  shaken  with  a  cold,  neutral,  or  slightly  acid  solution  of 
MnCl2,  does  not  precipitate  a  compound  of  manganese. 

Fusion  with  Na2CO3  and  KNO3  oxidizes  manganese  com- 
pounds to  green  salts  of  manganic  acid,  K2MnO4  and  Na2MnO4. 


Qualitative  Analysis  xi 

PbO2,  lead  dioxid,  boiled  with  H2SO4  and  a  little  of  a  man- 
ganese compound,  oxidizes  the  latter  to  permanganic  acid, 
HMnO4,  which  imparts  a  pink  or  purple  color  to  the  solution.  If 
a  chlorid  or  HC1  be  present  in  any  considerable  quantity  it  must 
be  removed  by  evaporating  with  concentrated  H2SO4  until  dense 
fumes  appear. 

ZINC 

NH4OH  produces  in  neutral  solutions  a  partial  precipitation 
of  Zn(OH)2,  white  and  gelatinous ;  soluble  in  ammonium  salts 
producing  double  salts  ;  changed  by  (NH4),S  into  ZnS. 

H,S  precipitates  ZnS,  white,  incompletely  from  neutral  solu- 
tions of  zinc  salts  of  the  inorganic  acids  ;  it  is  soluble  in  most 
dilute  acids,  but  is  only  slightly  soluble  in  acetic  acid,  and 
wholly  insoluble  in  a  solution  containing  an  alkalin  acetate,  as 
NaC2H3O2. 

(NH4)2S  precipitates  ZnS,  white. 

BaCO3,  when  shaken  with  a  cold,  neutral,  or  but  slightly  acid 
solution  of  ZnCl2,  does  not  precipitate  any  compound  of  zinc. 


ALUMINUM 

NH4OH  precipitates  A1(OH)3,  white,  gelatinous;  somewhat 
soluble  in  excess,  the  A1(OH)3  being  reprecipitated  by  heat. 

(NH4)2S  precipitates  A1(OH)3,  as  the  sulfid  is  decomposed  by 
water. 

BaCO3,  when  shaken  with  a  cold,  neutral,  or  slightly  acid  solu- 
tion of  A1C13,  precipitates  A1(OH)3  or  basic  carbonates. 


CHROMIUM 

NH4OH  precipitates  Cr(OH)3,  green,  gelatinous,  difficultly 
soluble  in  excess  and  reprecipitated  by  boiling. 

(NH4)2S  precipitates  Cr(OH)3. 

BaCO3,  when  shaken  with  a  cold,  neutral,  or  but  slightly  acid 
solution  of  CrCl3,  precipitates  Cr(OH)3  or  basic  carbonates. 

Fusion  with  KNO3  and  Na?CO3  oxidizes  chromium  compounds 
to  K2CrO4  and  Na,CrO4,  yellow.  If  the  fused  mass  is  dissolved 
in  water  and  the  solution  acidified  with  acetic  acid,  the  addition 
of  lead  acetate  precipitates  PbCrO4,  yellow. 


Xll 


Elementary  Chemistry 


IV.     AMMONIUM   CARBONATE   GROUP 

(The  Alkalin  Earth  Metals) 

METHOD  OF  ANALYSIS 

To  the  solution  add  NH4C1,  NH4OH,  and  then  (NH4).»CO: 
Warm,  and  if  a  precipitate  appears,  filter  and  wash. 


Precipitate:     BaCO3,  SrCO3,  CaCO3 

Pour  small  portions  of  warm  acetic  acid  upon  the 
ptt.,  avoiding  an  excess,  until  it  is  dissolved.  To  a 
small  portion  of  the  solution  add  K2Cr2O7,  and  if  a 
ptt.  appears  add  K2Cr2O7  to  all  of  the  solution,  and 
warm  and  filter. 


Precipitate  : 
BaCrO4 

Filtrate  : 

Sr(C2H302)2,  Ca(C2H302)2 

JliliCi    SUIJclUC 

of  the  test 
tube  with   a 
glass  rod.    A 

Dissolve  in 

Make   alkalin  with   NH4OH,  add 

crystalline 

HC1,    warm 

(NH4)2CO3   and  warm.     Filter  the 

ptt.    proves 

the    solution 

ptt.  (if  none  appears,  Sr  and  Ca  are 

the  presence 

and  add   a 
few  drops  of 

absent),  wash   thoroughly,  and  dis- 
solve  on    the    filter  with    the  least 

of  magne- 
sium. 

H2S04.      A 
white    ptt. 

possible  quantity  of  HC1.    Evaporate 
just  to  dryness,  dissolve  in  a  little 

(which,  how- 

water, filter  if  not  clear,  and  evapo- 

ever,   may 

rate  to  small  bulk.     Divide  into  two 

appear  yel- 

portions. 

low  from  tlic 

K2Cr2O7    in 

the  solution) 

PORTION  I 

PORTION  II 

proves  the 

SrCl2 

CaCl2 

presence   of 

Add    a  little 

Add    a    little 

barium. 

CaSO4,  heat  to 

K2SO4  and  heat  to 

boiling,    and    if 

boiling.     If  a   ptt. 

no  ptt.  appears 

forms,  filter  it  off 

• 

at  once  let  stand 

and  to  the  filtrate 

for  at  least  ten 

add  NH4OH  till 

minutes.    A  fine 

alkalin,      then 

white  ptt.  proves 

(NH4)2C2O4    and 

the  presence  of 

warm.      A    white 

strontium. 

ptt.    proves   the 

presence    of  cal- 

cium. 

Filtrate : 
Mg.  salt. 

AddNH4OH 

and 

Na2HP04. 
Rub      the 


Qualitative  Analysis  xiii 

REACTIONS  OF  SOLUTIONS  OF  BARIUM,  STRONTIUM, 
CALCIUM,  AND  MAGNESIUM  SALTS 

BARIUM 

Na-jCOg  or  (NH4)  CO3  precipitates  from  neutral  or  alkalin 
solutions  BaCO3,  white,  flocculent  at  first,  but  becoming  crystal- 
line when  gently  warmed.  BaCO3  is  very  slightly  soluble  in 
NH4C1;  freely  soluble  in  HC1  and  acetic  acid,  HC2H3O2,  with 
effervescence. 

H2SO5  precipitates  BaSO4,  white,  practically  insoluble  in 
water,  acids,  or  alkalis. 

Na2CO3  or(NH4)2CO3  precipitates  SrCO3,  resembling  BaCO3. 

STRONTIUM 

H2SO4  precipitates  SrSO4.  Calcium  sulfate,  although  but 
slightly  soluble  in  water,  is  more  soluble  than  SrSO4,  so  that 
CaSO4  will  precipitate  SrSO4  from  a  concentrated  solution  of  a 
strontium  salt.  Precipitation  is  more  complete  when  the  mixture 
is  warmed  or  when  a  concentrated  solution  of  K2SO4  is  used 
instead  of  the  CaSO4. 

K2CrO4  or  K2Cr2O7  does  not  precipitate  SrCrO4  from  dilute 
solutions  acidified  with  HC2H3O2. 

CALCIUM 

Na2CO3  or(NH4)2CO3  precipitates  CaCO3,  resembling BaCO3. 

K2CrO4  or  K2Cr2O7  produces  no  precipitate  in  dilute  solutions 
acidified  with  HC2H3O2,  since  CaCrO4  is  soluble  in  both  water 
and  HC2H302. 

(NH4)2C2O4  precipitates  CaC2O4,  white,  crystalline. 

H2SO4  or  a  soluble  sulfate,  as  K2SO4,  precipitates  CaSO4  only 
from  concentrated  solutions,  and  then  but  partially. 

MAGNESIUM 

NH4OH  precipitates  from  neutral  solutions  containing  no 
ammonium  salts  one-half  of  the  magnesium  as  Mg(OH)2.  The 
other  half  unites  with  the  ammonium  salt  which  is  formed  to 
produce  double  salts,  such  as  MgCl2  •  2NH4C1.  These  double 
salts  are  soluble  in  water  and  not  precipitated  by  NH4OH  or 
(NH4),CO3.  The  object  of  adding  NH4C1  in  the  analysis  is  to 
form  the  double  salt  and  thus  prevent  the  precipitation  of  the 
magnesium. 


XIV 


Elementary  Chemistry 


Na2HPO4  or  NaNH4HPO4  precipitates  from  solutions  of 
double  salts,  such  as  MgCl2'  2  NH4C1,  in  the  presence  of  NH4OH, 
MgNH4PO4,  white  and  crystalline.  Crystallization  may  be 
hastened  by  stirring  the  solution  with  a  glass  rod. 


V.     THE  ALKALI  METALS:     AMMONIUM,  SODIUM, 
POTASSIUM 

METHOD  OF  ANALYSIS 

Ammonia.  Put  a  little  of  the  original  substance  in  a  small 
beaker  and  add  NaOH.  Cover  the  beaker  with  a  watch  glass,  on 
the  under  side  of  which  is  placed  a  moistened  piece  of  red  litmus 
paper.  Heat  gently,  but  not  to  boiling.  If  the  litmus  paper 
turns  blue  the  presence  of  ammonia  is  proved. 

Sodmm  and  Potassium.  Evaporate  the  filtrate  from  the 
ammonium  carbonate  group  to  dryness  and  heat  until  no  more 
fumes  of  ammonium  salts  are  given  off.  Divide  the  residue  into 
two  portions. 


PORTION   I.     Sodium,    Potas- 

PORTION  II.      Potassium,  So- 

sium Salts. 

dium  Salts. 

Moisten  a  small  portion  with 

Dissolve    in    least    possible 

HC1,  slip  a  clean  platinum  wire 

amount  of  water  and  divide  solu- 

into it  and  introduce  into  the 

tion  into  two  portions. 

Bunsen  flame.     A  yellow  flame 

proves  the  presence  of  sodium  ; 

PORTION  I. 

PORTION  II. 

a  violet  flame  proves  the  pres- 
ence of  potassium. 
If  sodium    is  present,   view 
the  flame  through  a  blue  glass, 
whereby  the  yellow  rays  are 
cut  off,  but  the  violet  allowed 
to  pass. 

Add    platinum 
chlorid  solution 
and  keep  under 
observation  for 
some  time.     A 
yellow    ptt. 

Add  picric  acid 
solution.  A  yel- 
low ptt.  indi- 
cates presence 
of  potassium. 

^ 

proves    pres- 

ence of  potas- 

sittm. 

REACTIONS  OF  SOLUTIONS  OF  AMMONIUM,  POTASSIUM, 
AND  vSoDiuM  SALTS 


AMMONIA 

KOH  or  NaOH  when  warmed  with  an  ammonium  salt  liberates 
ammonia,  which  turns  moist  red  litmus  paper  blue. 

When   any  ammonium  salts  are  heated  they  break  up  into 


Qualitative  Analysis  xv 

volatile  constituents  so  that  through  heat  ammonia  may  be  sepa- 
rated from  non-volatile  substances. 

SODIUM 

Flame  test.  A  sodium  salt  introduced  into  a  Bunsen  flame  on 
a  platinum  wire  colors  it  an  intense  yellow. 

POTASSIUM 

Platinum  chlorid,  PtCl4,  produces  a  yellow  precipitate. 

Picric  acid  produces  a  yellow  precipitate. 

Flame  test.  A  potassium  salt  introduced  into  a  Bunsen  flame 
on  a  platinum  wire  colors  it  violet.  As  this  color  is  marked  by 
even  a  very  small  proportion  of  sodium,  if  that  element  is  present, 
the  flame  should  be  observed  through  blue  glass,  which  absorbs 
the  yellow  light. 

DETECTION  OF  ACIDS 

I.  BARIUM  CHLORID  GROUP 

Sulfuric  acid,  HoSO^,  precipitates  BaSO4,  white,  insoluble  in 
HC1. 

In  neutral  solution  phosphoric  acid,  H3PO4,  precipitates 
Ba3PO4,  white,  soluble  in  HC1. 

Sulfurous  acid,  H.,SO3,  precipitates  BaSO3,  white,  soluble  in 
HC1  with  evolution  of  SO2  (odor). 

II.  SILVER  NITRATE  GROUP 

Hydrochloric  acid,  HC1,  precipitates  AgCl ;  white  curds  very 
soluble  in  NH4OH. 

Hydrobromic  acid,  HBr,  precipitates  AgBr,  pale  yellow, 
slowly  soluble  in  NH4OH. 

Hydriodic  acid,  HI,  precipitates  Agl,  yellow,  very  slightly 
soluble  in  NH4OH. 

III.     SPECIAL  TESTS  FOR  SOME  COMMON  ACIDS 

Carbonates.  Most  carbonates  give  up  their  carbon  dioxid 
when  acted  upon  by  HC1  or  HNO3.  (See  Experiment  67.) 

Sulfids.  HC1  evolves  H2S  readily  from  the  sulfids  of  the 
alkali  and  alkalin  earth  metals,  and  from  sulfids  of  magnesium, 
manganese,  zinc,  and  iron;  less  readily  from  those  of  lead,  bis- 
muth, cadmium,  antimony,  tin,  nickel,  and  cobalt ;  from  other 
sulfids  with  difficulty  or  not  at  all. 


xvi  Elementary  Chemistry 

H2S  blackens  filter  paper  moistened  with  lead  acetate  solution. 

A  sulfid,  when  fused  with  a  small  piece  of  solid  NaOH  on  a 
crucible  cover,  forms  Na2S,  which,  when  moistened  and  placed  on 
a  silver  coin,  gives  a  black  stain  of  Ag2S. 

Acetates.  Concentrated  H2SO4  when  warmed  with  an  acetate 
liberates  acetic  acid,  HC2H3O2,  recognizable  odor.  (See  also 
ethyl  acetate,  Experiment  221.) 

In  neutral  solution  FeCl  gives  a  dark  red  color  to  a  solution 
of  an  acetate. 

Nitrates.     (See  Experiment  129.) 


APPENDIX  B 

THE  METRIC  SYSTEM  OF  WEIGHTS  AND 
MEASURES 

The  metric  system  of  weights  and  measures  is 
employed  in  the  affairs  of  everyday  life  in  most  of  the 
countries  of  continental  Europe,  and  is  almost  exclu- 
sively used  in  science. 

The  fundamental  unit  is  the  meter,  which  is  a  unit 
of  length  a  little  over  a  yard  long.  The  other  units  of 
length  are  derived  from  the  meter  by  successively 
multiplying  and  dividing  it  by  ten.  The  names  of 
these  derived  units  are  indicated  by  prefixes.  Thus, 
the  multiple  prefixes  are  the  Greek  words  for  ten, 
deca-,  hundred,  hecto-,  and  thousand,  kilo-,  and  the  sub- 
multiple  prefixes  are  the  Latin  words  for  ten,  deci-, 
hundred,  centi-,  and  thousand,  milli—. 

The  unit  of  weight  or  mass  is  the  gram,  which  is  the 
weight  of  a  cubic  centimeter  of  water  at  4°.  The  same 
prefixes  as  are  given  above  are  used  in  expressing  the 
names  for  the  multiples  and  sub-multiples  of  the  gram. 

The  unit  of  volume  is  the  liter,  which  is  the  volume 
occupied  by  1,000  cubic  centimeters  (one  cubic  deci- 
meter of  water);  1,000  grams  (one  kilogram)  of  water 
occupies  one  liter  at  4°. 

In  this  system  fractions  must  always  be  expressed 
decimally,  and  only  one  unit  should  be  employed  in 
designating  a  quantity  measured.  Thus,  the  fractions 
%,  /3,  %,  etc.,  are  written  0.5,  0.33,  0.75,  and  so  on. 
Also  the  weight  of  an  object  is  not  given  as  nine  grams, 
four  decigrams,  and  six  centigrams,  even  when  abbre- 
viated into  9^-,  4^-,  and  6^-,  but  should  be  written  9.46^. 

[  xvii  1 
2b 


XV111 


Elementary  Chemistry 


The  relations  between  the  units,  multiples,  and  sub- 
multiples  of  the  metric  system  are  shown  in  the 

TABLE  OF  THE  METRIC  SYSTEM 


Length 

Weight 

Volume 

Notation 

Kilometer 

Kilogram 

Kiloliter      _   . 

IOOO. 

Hectometer 

Hectogram  

Hectoliter  

IOO. 

Decameter 

Decagram 

Decaliter 

10. 

METER 

GRAM 

LITER 

i  . 

Decimeter 

Decigram   . 

Deciliter  

O.  I 

Centimeter 

Centigram  

Centiliter  

O.OI 

Millimeter 

Milligram 

Milliliter 

O.OOI 

It  is  evident  from  the  table  that  10  millimeters  equal 
one  centimeter,  10  centimeters  equal  one  decimeter,  10 
decimeters  equal  one  meter,  10  meters  equal  one  hecto- 
meter, and  10  hectometers  equal  one  kilometer.  Anal- 
ogous statements  are  true  for  the  units  of  weight  and 
volume. 

The  abbreviations  most  often  used  in  this  book  are : 
cm-  for  centimeter ;  c-c-  for  cubic  centimeter  ;  L  for  liter  ; 
and  ^-  for  gram. 

The  relations  of  the  weights  and  measures  of  the 
metric  system  to  the  weights  and  measures  commonly 
used  in  English-speaking  countries  are  shown  by  the 

TABLE  OF  METRIC  EQUIVALENTS 

inches 

mile 

inch 

liquid  quart 

grains 

pounds  (Avoir.) 

pounds 

centimeters 

kilometers 

cubic  centimeters 

liter 

kilogram 

grams 


One  meter 

One  kilometer 

One  centimeter 

One  liter 

One  gram 

One  kilogram 

One  metric  ton  

One  inch 

One  mile 

One  cubic  inch 

One  liquid  quart  . . . 
One  pound  (Avoir.). 
One  ounce  .. 


39-37 
0.62 

0-39 
i  .06 

15-43 

2204 

2-54 
1.61 

16.39 
0-95 
0-45 

28.35 


One  grain  (Apoth  ). 


z=        0.0648  gram 


APPENDIX  C 


\2I2° 


INSTRUMENTS  FOR  WEIGHING  AND 
MEASURING 

The  Thermometer.  The  thermometer  is  an  in- 
strument for  measuring  temperatures.  Its  action  de- 
pends upon  the  fact  that  liquids  expand 
when  heated,  and  contract  when  cooled. 
The  liquids  in  common  use  are  mercury 
or  alcohol  ;  water  is  not  suitable,  as  it 
freezes  at  too  high  a  temperature. 
Chemical  thermometers  (Fig.  a)  consist 
of  a  glass  tube  with  minute  bore,  which 
is  blown  out  into  a  bulb  at  the  end.  The 
bulb  is  almost  invariably  made  cylindri- 
cal in  shape  so  that  the  thermometer 
may  be  thrust  through  a  cork  closing  a 
flask,  test  tube,  or  bottle,  the  tempera- 
ture of  the  interior  of  which  is  to  be 
found.  Details  as  to  the  making  of  ther- 
mometers cannot  be  gone  into  here,  but 
brief  mention  may  be  made  of  the 
method  employed  in  graduating  the 
instrument. 

The  bulb  is  placed  in  a  dish  filled 
with  melting  ice,  and  the  position  of  the 
liquid  in  the  stem  marked  on  the  glass. 
The  instrument  is  then  placed  in  steam 
issuing  from  water  which  is  kept  briskly 
boiling  under  a  pressure  of  one  atmos- 
phere. The  liquid  expands  much  more  than  does  the 
glass  and  rises  in  the  stem.  This  new  position  is  also 

[xix] 


Fig.  a  — 

THERMOMETERS 


XX 


Elementary  Chemistry 


marked  on  the  glass.  The  portion  of  the  stem  between 
the  points  thus  fixed  is  divided  into  a  certain  number  of 
equal  parts,  the  number  depending  upon  what  scale  is 
adopted.  The  stem  above  and  below  these  fixed  points 
is  likewise  divided  into  parts  which 
are  equal  to  those  between  the  two 
fixed  points. 

In  the  Centigrade  scale,  which 
is  in  general  use  in  continental 
Europe,  and  in  almost  exclusive 
use  among  scientists,  the  interval 
between  the  temperature  of  melt- 
ing ice  and  boiling  water  is  divided 
into  100  equal  parts  ;  the  lower  tem- 
perature is  set  at  o°  and  the  higher 
at  100°.  The  Centigrade  scale  alone 
is  employed  in  this  book. 

In  the  Fahrenheit  sca/e,  which  is 
in  general  use  in  English-speaking 
countries,  the  interval  between  the 
fixed  points  is  divided  into  180 
equal  parts,  and  the  temperature  of 
melting  ice  is  set  at  32°  and  that  of 
boiling  water  at  212°. 

The  value  of  a  Centigrade  degree 
is  1.8  times  that  of  a  Fahrenheit  de- 
gree, and  32°  Fahrenheit  marks  the 
same  temperature  as  o°  Centigrade. 
To  convert  degrees  C.  into  de- 
grees F.,  multiply  by  1.8  and  add 32.  To  convert  degrees 
F.  into  degrees  C.,  subtract  32  and  divide  by  1.8. 

The  Barometer.  The  barometer  is  used  for  meas- 
uring the  pressure  of  the  atmosphere.  In  its  simplest 
form  it  consists  of  a  straight  glass  tube,  about  a  meter 
long  and  closed  at  one  end.  This  is  completely  filled 


Fig.  6  —  A  SIMPLE 

BAROMETER 


Instruments  for  WcigJiing  and  Measuring 

with  mercury,  which  is  boiled  in  the  tube  in  order  to 
drive  out  every  trace  of  air  or  moisture,  and  its  open 
end  then  placed  under  the  surface  of  mercury  in  a  dish 
(Fig.  b).  The  mercury  falls  in  the  tube  to  a  height  of 
about  fj6cm-.  The  liquid  does  not  all  run  out  of  the  tube 
because  the  atmosphere  pressing-  down  upon  the  mer- 
cury in  the  dish  pushes  it  up  until  the  weight  of  liquid 
in  the  tube  exactly  balances  the  pressure  of  the  atmos- 
phere. If  for  any  cause  the  pressure  of  the  atmosphere 


Fig.  C A    TRIP    BALANCE 

becomes  greater,  it  will  push  the  mercury  higher  up  in 
the  tube  ;  and  in  a  similar  fashion,  if  the  atmospheric 
pressure  becomes  less,  it  cannot  support  so  long  a  column, 
and  accordingly  the  liquid  in  the  tube  falls  somewhat. 
The  Balance.  The  balance  serves  to  find  the 
weight  of  an  object.  When  the  weight  is  to  be  ascer- 
tained only  to  tenths  of  grams,  the  form  of  balance 
known  as  the  "  trip  "  (Fig.  r)  is  excellent.  The  weights 
accompanying  need  have  no  pieces  less  than  5^-,  as  the 
beam  and  sliding  weight  in  the  front  permit  of  the 
weighing  to  tenths  of  grams  up  to  5  £"•. 


XX11 


Elementary  Chemistry 


In  the  quantitative  work  of  this  book,  a  balance 
weighing  to  hundredths  of  grams  at  least  is  required. 

Balances  sensi- 
tive to  a  milli- 
gram are  even 
better,  but  are 
much  more  ex- 
pensive and  must 
be  enclosed  in  a 
glass  case  to  pre- 
vent currents  of 
air  from  making 
them  work  too 
erratically.  Either 
an  equal-armed 

balance  (Fig.  d)  or  an  unequal-armed  one  (Fig.  e)  may 
be  used.  Of  the  former  there  are  numerous  excellent 
makes  on  the  market.  They  require  the  use  of  a  box  of 
weights  contain- 
ing tenths  and 
hundredths  of 
grams. 

The  form  of 
balance  in  Fig.  e 
was  devised  by 
the  author  for  the 
quantitative  work 
of  the  elementary 
chemistry  labor- 
atory. Its  advan- 
tages are  ease  in 
moving  about, 
rapidity  of  weigh- 
ing, and  "  non-losableness  "  of  the  weights,  which  are 
rings  moving  along  the  beam. 


Fig.  e UNEQUAL-ARMED    BALANCE 


Instruments  for  Weighing  and  Measuring    xxiii 


RULES  TO  BE  OBSERVED  IN  WEIGHING 


Fig.  g— 


1.  Always  leave  the  balance  and  weight 
in  a  clean  and  usable  condition. 

2.  Never   handle    the    zv  eights   with   the 
fingers  ;   use  forceps. 

^Fris^  3.    Do  not  vveigh  anything  but 

metals  (mercury  and  sodium  ex- 
cepted)  on  the  bare  scale  pan. 
Liquids  should  be  weighed  in  a 
dish  or  a  beaker,  the  weight  of 
which  has  already  been  found. 
Solids  should  be  placed  on  a 
piece  of  paper  creased  twice  at 

.        1,1  •        I  CIJU1INU1SK 

right  angles  so  as  to  sink  in 
a  little  at  the  center  (Fig.  c). 

Graduated  Vessels.  For  measuring 
rather  large  volumes  of  liquids  graduated 
cylinders  (Figs,  f  and  g)  of 
250  c-c-  or  50  c-c-  capacity  are 
used.  Volumetric  flasks 
(Fig.  li)  are  also  employed. 
For  measuring  small  vol- 
umes of  liquids  pipettes 
(Fig.  i)  and  burettes  (Fig. 
54,  page  77)  are  used.  Pip- 
ettes are  usually  graduated 
to  deliver  $c-c-t  ioc-c-,  2$c-c-t 

or  50  c-c-.     In  using  a  pipette,  its  tip  is 

dipped   into   the   liquid,    which   is   then 

sucked    up    nearly    to    the    top    by    the 

mouth,  and  the  upper  opening  quickly 

closed  with  the  finger.    By  lifting  up  the 

fore  finger  so  as  to  let  air  into  the  upper 

Fig.  h—  VOLU- 

part  of   the  pipette  the  liquid  may  be       METRIC  FLASK 


Fig.  f— 2 50 c-c 

CYLINDER 


XXIV 


Elementary  Chemistry 


made  to  drop  out  until  its  level  comes  even  with  the 
mark  on  the  stem.     The  definite  volume  of  liquid 
thus  measured  may  then  be  delivered  into  the 
vessel  in  which  it  is  to  be  used. 

Burettes  are  usually  graduated  into  tenths  of 
cubic  centimeters  and  may  hold  either  25  c-c-  or 
50  c.c.  •  but  as  sometimes  the  spaces  are  divided 
into  0.2  c-c-,  that  is,  fifths  of  a  cubic  centimeter, 
a  burette  should  be  carefully  examined  before  it 
is  used  in  order  that  it  may  be  read  correctly 
according  to  its  scale  of  division.  They  are 
clamped  vertically  to  a  support  and  rilled  by 
pouring  in  the  liquid.  Enough  liquid  is  allowed 
to  run  out  by  opening  the  clamp  to  drive  out  all 
air  in  the  delivery  tube,  and  then  by  noting  the 
reading  of  the  level  of  the  liquid  in  the  burette, 
the  required  volume  may  be  run  out  into  the 
vessel  being  used. 

A  convenient  stopcock  consists  of  a  glass  bead 
made  from  a  rod  a  little  larger  in  diameter  than 
the  bore  of  the  bit  of  rubber  tubing  attached  to 

the  burette.  This  bead  is 
slipped  into  the  rubber 
tube  between  the  burette  pjg.  i 
and  the  delivery  tip.  By  PIPETTE 
squeezing  the  rubber  a  little, 
a  channel  is  formed  between  it 
and  the  bead,  through  which  the 
liquid  in  the  burette  may  flow. 
The  size  of  this  channel  can  be 
regulated  with  such  ease  that 
the  liquid  may  be  delivered 
with  great  nicety. 

The  surface  of  liquids  which 
zvct  glass  is  curved  upward  near 


C 


Fig.  j  —  READING  A  BURETTE 

The  correct  reading  is  along  C. 

Readings  such  as  A  and  B  must 

not  be  taken 


Instruments  for  Weighing  and  Measuring     xxv 

the  glass  so  that  in  small  tubes  the  surface  is  concave. 
The  name  of  meniscus  has  been  given  to  this  curved 
surface.  The  position  of  a  liquid  surface  with  respect 
to  a  scale  is  always  reckoned  at  the  lowest  point  in  the 
meniscus,  and  the  eye  should  be  placed  so  that  a  line 
passing  from  it  to  the  tube  is  perpendicular  to  the  tube 
(Fig.y).  In  the  case  of  liquids  which,  like  mercury,  do 
not  wet  glass,  the  meniscus  is  convex,  and  readings  are 
taken  at  its  highest  point. 

It  is  a  good  plan  for  the  student  to  determine  the 
capacity  of  his  test  tubes,  beakers,  and  flasks  by  pouring 
water  into  them  from  one  of  the  above  vessels.  Their 
volume  once  determined,  no  time  is  lost  in  ascertaining 
what  size  of  beaker,  flask,  or  test  tube  is  to  be  used  in 
the  experiments  ;  they  may  also  serve  as  rough  and 
ready  measuring  vessels. 


NAME  OF 

ELEMENT 


APPENDIX  D 

TABLE  I  —  PHYSICAL  CONSTANTS  c 


Name  of  Discoverer  and 
Date  of  Discovery 


Aluminum 
Antimony .. 

Argon  

Arsenic  ... 

Barium  .. 


Bismuth  ... 
Boron 

Bromin 

Cadmium  .. 
Calcium 

Carbon 

Chlorin 

Chromium  . 

Cobalt 

Copper 

Fluorin 

Gold 

Hydrogen . . 

lodin 

Iron  _ 

Lead.. 

Lithium 

Magnesium 
Manganese. 

Mercury 

Nickel 

Nitrogen . . . 

Oxygen  

Phosphorus 
Platinum . . . 
Potassium.. 

Silicon 

Silver 

Sodium 

Strontium  „ . 

Sulfur 

Tin....    ... 

Zinc  . . 


Wohler (1827) 

Basil  Valentine (1460) 

Ramsay  and  Rayleigh...(i894) 
Albert  Magnus (isth  cent.) 

Davy (1808) 

Basil  Valentine (isth  cent.) 

Gay-Lussac  and  Thenard  (1808) 

Balard (1826) 

Stromeyer -(1841) 

Davy ...(1808) 

Known  from  earliest  times 

Scheele (1774) 

Vauquelin _ (i?97) 

Brand (i?35) 

Known  from  earliest  times..... 

Moissan (1886) 

Known  from  earliest  times 

Cavendish (J776) 

Courtois (1812) 

Known  from  earliest  times 

Known  from  earliest  times.  _. 


Liebig  and  Bussy (1830) 

Gahn  and  John (1807) 

Known  from  earliest  times 

Cronstedt (I75I) 

Rutherford (1772) 

Priestley. (1774) 

Brand (1674) 

Waston ( 1 750) 

Davy (1807) 

Berzelius (1823) 

Known  from  earliest  times 

Davy (1807) 

Davy  .    (1808) 

Known  from  earliest  times 

Known  from  earliest  limes 

centnrv   . 


TABLES 

SOME  OF  THE  ELEMENTS 


Atomic  Weights 

Valence 

Melting 
Point 

Boiling 
Point 

Specific 
Gravity  i 

H=  i 

O  =  16 

Approxi- 
mate 

26.9 
II9-3 
39-6 

27.1 
1  2O.  2 
39-9 

27 
1  20 
40 

III 
III,  V 

700  (?) 
440 

7 
i30o(?) 

2.67 
6.72 

74-4 

75-0 

75 

III,  V 

446-457 

Red  heat 

5.69 

136.4 

137-4 

137 

II 

Above  that 
of  cast  iron 

? 

3-75 

206.9 

208.5 

208 

III,  V 

268 

1700 

9.9 

10.9' 

II. 

ii 

III 

In  electric 
furnace 

p 

2.6 

79-36 

79.96 

80 

I 

—7-3 

63 

3  •  i  (liq-) 

in.  6 

112.4 

112 

II 

320 

770 

8.72 

39-8 

40.1 

40 

II 

Red  heat 

? 

i.  6-1.  8 

11.91 

12.  OO 

12 

IV 

? 

?  \ 

Diamond  3.5 
Graphite  2.2 

( 

Charcoal  1.5 

35-18 

35-45 

35-5 

I 

—  IO2 

—34 

1-33  (Hq-) 

5i-7 

52.1 

52 

II,  III 

? 

? 

6-7 

58.56 

59-o 

59 

II 

1800 

p 

8.6 

63-1 

63-6 

63-5 

I,  II 

1050 

? 

8.9 

18.9 

19. 

19 

I 

? 

195  7 

197.2 

197 

III 

1030 

? 

19-3 

1.  000 

1.008 

i 

I 

—  252.5 

i 

125.90 

126.85 

127 

I 

114 

120 

4-95 

55-5 

55-9 

56 

II,  III 

1  100 

? 

7.88 

205.35 

206.9 

207 

II,  IV 

325 

? 

n-37 

6.98 

7-03 

7 

I 

1  80 

? 

o-59 

24.18 

24-36 

24 

II 

750 

IIOO 

i-75 

54-6 

55.0 

55 

II 

7-2 

198.5 

200.  o 

200 

I,  II 

—38.9 

357 

13-59 

58.3 

58.7 

58-5 

II 

1600 

? 

8.9 

13-93 

14.04 

14 

III,  V 

—203 

—194 

13-93 

15.88 

16.00 

16 

II 

—  1825 

15.88 

30.77 

31.0 

3i 

III,  V 

44-2 

287] 

Yellow  1.83 
Red        2.21 

193  3 

194.8 

195 

IV 

2000 

? 

21-5 

38.86 

39-15 

39 

I 

62.1 

667 

4-9 

28.2 

28  4 

28 

IV 

Above  cast 
iron 

? 

2-5 

IO7.  12 

107-93 

108 

I 

1000 

? 

10.5 

22.88 

23-05 

23 

I 

97-6 

742 

0.97 

86.94 

87.6 

87 

II 

Red  heat 

? 

2-5 

31.83 

32.06 

32 

IIJV,VI 

II4-5 

448 

2.O 

118.1 

119.0 

119 

II,  IV 

227 

1600 

7-3 

64-9 

65-4 

65 

II 

420 

930 

7-i 

1  Referred  to  water  if  the  element  be  "in  a  solid  or  a  liquid  state ;  to 
hydrogen  if  in  a  gaseous  state. 

f  xxvii  ] 


xxviii  Elementary  Chemistry 

TABLE  II — TENSION  OF  WATER  VAPOR 


15° 

12  jmm. 

21° 

2O  nmm. 

16°   . 

1  3.  5  mm. 

24 

22  2  mm. 

17°  

14  ^.mm. 

25° 

23.(>mm. 

18° 

l^.^tnm. 

26° 

25  omm. 

IQ° 

1  6  2>mm- 

27° 

26  $  mm. 

2O°  

17  ^mm. 

28° 

28.1  mm. 

21°  

l8.$mm. 

29°  

2g.8m"'- 

ig  -jmm. 

-}0° 

aj  tm/Jt. 

TABLE  III  —  SOLUTIONS  TO  BE  PREPARED 

The  figures  in  parentheses  indicate  the  number  of  cubic  centi- 
meters (if  the  substance  is  a  liquid)  and  the  number  of  grams  (if 
the  substance  is  a  solid)  that  are  to  be  dissolved  in  water  ;  the 
solution  should  then  be  diluted  to  one  liter. 


Acetic  acid,  (140)  of  80$  acid. 

Alum  (any  one),  (100). 

Aluminum  chlorid,  (TOO). 

Aluminum  sulfate,  (25). 

Ammonium  carbonate.  Dis- 
solve 2OO&-  in  a  mixture  of 
IOQC.C.  of  cone.  NH4OH  and 
600  c.c.  of  water,  and  after  solu- 
tion is  complete  dilute  to  one 
liter. 

Ammonium  chlorid,  (100). 

Ammonium  hydroxid,  (250)  of 
cone.  NH4OH. 

Ammonium  molybdate.  Dis- 
solve so.?"'  of  molybdic  acid  in 
a  mixture  of  IOQC.C.  of  cone. 
NH4OH  and  150^.  of  water. 
Dilute  250 c.c.  of  cone,  nitric 
acid  with  500  c-c-  of  water  and 
pour  into  first  solution  slowly 
and  with  constant  stirring. 
Let  stand  in  a  warm  place  for 
48  hours  and  decant  the  clear 
supernatant  solution  for  use. 


Ammonium  nitrate,  (25). 

Ammonium  oxalate,  (50). 

Ammonium  polysulfid.  Dis- 
solve some  sulfur  in  ammo- 
nium sulfid  solution. 

Ammonium  sulfid.  Pass  H2S 
into  one  liter  of  cone.  NH4OH 
to  saturation.  Then  add 
750  c.c.  cone.  NH4OH  and  one 
liter  of  water. 

Ammonium  sulfocyanid  (also 
called  thiocyanate),  (10). 

Antimony  chlorid.  Dissolve 
25«£"-  in  a  mixture  of  250 c.c. 
of  cone.  HC1  and  750^-  of 
water. 

Arsenic  chlorid.  Dissolve  50^- 
sodium  arsenite,  Na3AsO3, 
in  i  ,ooo<^-  of  water  and  add  in 
small  portions  cone.  HC1  until 
further  addition  occasions  no 
effervescence. 

Barium  carbonate.  In  suspen- 
sion in  water. 


Tables 


XXIX 


Barium  chlorid,  (60). 

Barium  hydroxid.  Dissolve  50^"- 
in  one  liter  of  hot  water,  let 
stand  over  night,  and  filter  or 
decant.  Keep  in  tightly 
stoppered  bottle. 

Bismuth  nitrate,  (25).  The  solu- 
tion must  contain  a  little  free 
nitric  acid. 

Boric  acid,  (40).  Saturated  solu- 
tion. 

Bromin  solution.  Dissolve  2^- 
of  KBr  in  250^-  of  water, 
add  6<f-  (2  c.c.)  of  bromin,  and 
shake  until  bromin  is  dis- 
solved. 

Bromin  water.  Put4o«?"-(i3^-) 
in  a  liter  of  water.  Keep  bot- 
tle tightly  stoppered  and  in 
the  dark. 

Cadmium  chlorid,  (25). 

Calcium  chlorid,  (25). 

Calcium  hydroxid,  (lime  water). 
Put  some  freshly  slaked  lime 
in  a  bottle,  fill  bottle  with 
water,  shake,  and  when  solu- 
tion is  clear,  decant  and  reject 
it,  as  it  may  contain  some 
impurities  from  the  lime. 
Fill  the  bottle  with  water 
again  and  shake  well. 

Calcium  sulfate.  Prepare  satu- 
rated solution  in  same  manner 
as  lime  water  above. 

Chromium  chlorid,  (25).  To 
I,OOQC.C.  of  potassium  dichro- 
mate  solution  add  50  c.c.  of 
cone.  HC1  and  25  c.c.  of  alco- 
hol. Boil  for  half  an  hour 
gently  and,  if,  after  standing 
over  night,  the  solution  is  not 


clear  green  add  more  alcohol 
and  boil  again. 

Chromium  sulfate,  (30). 

Chlorin  water.  Pass  chlorin 
gas  into  water  until  it  smells 
strongly  of  the  gas.  Better 
make  small  quantities  when 
needed  by  adding  a  little 
cone.  HC1  to  a  few  crystals  of 
KC1O3  in  a  test  tube  and  as 
soon  as  the  gas  escapes  from 
mouth  of  tube,  adding  water 
to  stop  reaction. 

Cobalt  chlorid,  (50). 

Cobalt  nitrate,  (35). 

Cochineal.  Grind  a  little  with 
water  and  dilute  to  desired 
tint. 

Copper  nitrate,  (40). 

Copper  sulfate,  (35). 

Disodium  hydrogen  phosphate, 
(120). 

Ferric  chlorid,  (100). 

Ferrous  sulfate.  Dissolve  150^- 
of  clear  crystals  in  one  liter 
of  water,  and  add  5  c.c.  of  cone. 
H2SO4  and  a  few  pieces  of 
iron  (tacks  or  small  nails). 

Hydrochloric  acid,  (250)  of  cone, 
acid. 

Indigo.  Slowly  add  lotf-  of 
powdered  indigo  to  25  c.c.  of 
fuming  sulfuric  acid.  Let 
stand  for  a  day  and  then  add 
slowly  with  constant  stirring 
to  one  liter  of  water. 

Lead  acetate,  (90). 

Lead  nitrate,  (40). 

Litmus.  Grind  a  little  with 
water  to  a  paste  and  dilute  to 
desired  tint. 


XXX 


Elementary  Chemistry 


Magnesium  chlorid,  (25). 

Magnesium  sulfate,  (100). 

Manganous  chlorid,  (75). 

Manganous  sulfate,  (35). 

Mercuric  chlorid,  (30). 

Nessler's  Reagent.  Dissolve 
35^"-  of  potassium  iodid  in 
IQQC.C.  of  water  ;  also  dissolve 
i6&-  of  mercuric  chlorid  in 
300^-  of  water.  Add  the 
latter  solution  to  the  former 
slowly  with  constant  stirring 
until  the  precipitate  ceases  to 
be  redissolved.  Then  add  a 
solution  of  65 &•  of  potassium 
hydroxid  in  60  c.c.  of  water 
and  filter.  Put  the  solution 
into  a  number  of  small  bottles 
and  cover  the  corks  with  par- 
affin. Keep  in  a  cool,  dark 
place,  and  when  the  solution 
is  needed,  do  not  open  more 
than  one  bottle  at  a  time. 

Nickel  chlorid,  (25). 

Nickel  nitrate,  (35). 

Nitric  acid,  (250)  of  cone.  acid. 

Phenolphthalein.  Dissolve  one 
gram  in  100  c.c.  of  alcohol  and 
dilute  with  water  until  a  pre- 
cipitate begins  to  form  ;  then 
add  enough  alcohol  to  clarify 
solution. 

Platinum  chlorid.  Use  com- 
mercial solution,  or,  dissolve 
scrap  platinum  in  aqua  regia, 
evaporate  nearly  to  dryness, 
and  dissolve  residue  in  enough 
water  to  make  about  16  per 
cent  solution. 


Potassium  bromid,  (30). 

Potassium  chromate,  (100). 

Potassium  chlorid,  (50). 

Potassium  dichromate,  (50). 

Potassium  ferricyanid,  (30). 

Potassium  ferrocyanid,  (50). 

Potassium  hydroxid,  (150). 

Potassium  iodid,  (25). 

Potassium  nitrate,  (100). 

Potassium  sulfate,  (100). 

Potassium  sulfocyanate,  (50). 

Silver  nitrate,  (40).  Keep  in 
amber  glass  bottle. 

Sodium  acetate,  (130). 

Sodium  ammonium  phosphate, 
(70). 

Sodium  chlorid,  (100). 

Sodium  hydroxid,  (175). 

Sodium  sulfite,  (200). 

Stannous  chlorid.  Dissolve 
$og-  in  100^-  of  hot  cone. 
HC1  and  keep  a  few  pieces  of 
tin  in  the  solution.  Make 
only  when  needed,  as  it  does 
not  keep  well. 

Starch  paste.  Grind  about 
io<f-  to  a  paste  with  a  little 
cold  water,  then  boil  with 
250  c.c.  of  water  until  clear. 

Strontium  chlorid,  (30). 

Strontium  nitrate,  (30). 

Sulfuric  acid,  (250)  of  cone.  acid. 
Pour  acid  in  small  portions, 
with  stirring,  into  the  full 
amount  of  water  required  for 
dilution. 

Tartar  emetic,  (100). 

Zinc  chlorid,  (50). 

Zinc  sulfate,  (140). 


APPENDIX  E 

SIGNIFICANT    FIGURES    AND    FORMS    OF 
RECORD   IN   QUANTITATIVE   WORK 

All  the  figures  of  a  number  are  called  significant 
excepting-  the  ciphers  at  the  right  of  a  whole  number 
and  the  ciphers  at  the  left  of  a  decimal  fraction  ;  thus, 
the  significant  figures  of  30,600  as  well  as  of  0.000306 
are  306. 

In  all  measurements  one  significant  figure  more  than 
is  known  to  be  correct  is  kept  in  the  number  express- 
ing the  result  of  the  measurement ;  this  figure  is  said 
to  be  the  least  accurate  figure  or  the  doubtful  figure  of 
the  number.  Thus,  suppose  the  volumes  of  water  dis- 
placed from  an  aspirating  bottle  in  three  determinations 
of  the  weight  of  a  liter  of  oxygen  (Experiment  16)  were 
found  to  be  in  each  case,  1685  *•*•,  1680^-,  and  1689^-  ; 
the  sum  of  these  three  numbers  is  5054,  and  their  mean 
is  1684.666  -f  «*•,  or  1684.66!^-,  or  1684.67^-.  No  one 
of  these  is  proper,  for  each  assumes  a  greater  accuracy 
than  we  have  any  warrant  for  ;  moreover,  the  second  is 
irrational  in  its  combining  a  common  with  a  decimal 
fraction.  The  three  determinations  differ  in  units' 
place  ;  hence,  we  are  not  sure  of  units'  place.  We  must 
accordingly  drop  the  entire  decimal  part  of  the  average 
number  ;  but  as  the  decimal  is  greater  than  0.5,  it  is 
customary  to  change  the  figure  4  in  the  average  to  5,  so 
that  the  average  is  1685.  If  the  decimal  had  been  less 
than  5,  it  would  have  been  dropped,  and  the  average 
would  have  remained  1684. 

[  xxxi  ] 


xxxii  Elementary  CJiemistry 

Again,  suppose  that  in  three  weighings  of  a  dish  the 
following  results  were  obtained:  24.33^"-,  24.35<?"-,  an(^ 
24.32^-.  The  sum  of  these  numbers  is  73.00,  and  their 
average  arithmetically  may  be  24.3333  -f  or  24.33-!-,  but 
if  the  above  rules  be  observed,  the  average  must  be 
24.33.  It  is  to  be  noted  that  the  sum  is  given  as  73.00 
and  not  as  73.  By  writing  the  two  ciphers  in  the  deci- 
mal we  indicate  that  we  know  that  the  tenths  and  hun- 
dredths  are  zero,  while  the  73  without  the  ciphers  leaves 
us  in  doubt. 

Let  another  illustration  emphasize  this  last  point. 
Suppose  the  weight  of  a  vessel  be  found  on  a  balance 
sensitive  to  a  hundredth  of  a  gram,  but  that  neither  the 
tenths  nor  the  hundredths  gram-weights  are  needed 
to  secure  equilibrium.  If  only  the  ten-  and  two-gram 
weights  are  on  the  pan  of  the  balance,  its  weight  is 
written  12.00^-  and  not  just  12?-.  The  ciphers  indicate 
the  degree  of  accuracy  attained.  They  mean  that  the 
tenths  and  hundredths  were  tried  in  determining  the 
weight,  but  were  not  needed.  By  expressing  a  weight 
as  12.00^-  you  indicate  that  a  balance  sensitive  to  hun- 
dredths of  grams  was  used,  while  12.0^-  would  mean 
that  a  balance  sensitive  only  to  tenths  of  grams  was 
employed. 

In  the  directions  for  the  quantitative  experiments 
the  degree  of  accuracy  is  denoted  by  the  number  of 
decimal  places  kept  in  specifying  a  quantity  to  be  taken. 
Thus,  in  Experiment  46,  exactly  2.00  &•  are  specified, 
which  means  that  on  a  balance  sensitive  to  hundredths 
of  grams,  two  grams,  and  not  more  or  less  by  a  hun- 
dredth of  a  gram,  are  to  be  taken.  In  Experiment  16 
the  directions  are  to  take  about  5  z-  of  manganese  dioxid. 
This  quantit)^  may  be  weighed  roughly,  that  is,  to  about 
a  gram,  it  making  no  difference  if  4^-  or  6<f-  should  hap- 
pen to  be  taken.  If  the  amount  had  been  written  5.0^-, 


Significant  Figures  and  Forms  of  Record   xxxiii 

it  would  have  been  necessary  to  use  a  more  sensitive 
balance  and  weigh  to  tenths  of  grams. 

Suppose  that  it  were  found  that  2.68^-  of  oxygen 
occupied  a  volume  of  1,871  c-c-y  i.  e.,  1.871  /-.  Then  the 
quotient  of  2.68  divided  by  1.871  gives  the  weight  of  one 
liter.  The  question  arises  :  How  many  figures  of  the 
quotient  are  to  be  retained  ?  It  is  apparent  that  if  only 
weighings  to  hundredths  of  grams  were  made,  then 
only  hundredths  should  be  kept.  Accordingly  the 
quotient  is  1.43. 

Arithmetical  operations  on  data  obtained  in  quanti- 
tative experiments  may  be  much  abbreviated,  with  no 
loss  in  accuracy,  by  dropping  after  an  operation  of  mul- 
tiplication or  division  all  except  the  significant  figures 
in  a  number. 

To  illustrate,  let  us  solve  the  following  problem  : 
Find  the  reduced  volume  of  283  c-c-  of  a  gas  measured 
at  662  mm-  and  22°. 

It  is  to  be  noted  that  no  one  of  the  three  numbers 
given  has  more  than  three  figures  ;  hence,  there  are 
only  three  significant  figures.  Substituting  in  the  for- 
mula (§  27),  we  have 


Below  are  given  two  calculations  of  the  value  of  V, 
the  one  to  the  right  retaining  all  figures  after  each  mul- 
tiplication, the  one  to  the  left  retaining  in  each  product 
only  three  (significant)  figures. 

283  283 

273  273 

849  849 

1981  1981 

566  566 

77259  77259 

3b 


XXXIV 


Elementary  Chemistry 


773 
662 


1546 
4638 

4638 
511726 

295 
760 

17700 
2065 

224200 

224)512(228.5 

"  448 
640 
448 


1920 
1792 
1280 


77259 
662 


463554 
463554 

5H45458 


295 
760 


17700 
2065 

224200 

224200)51145458, 
4484 

6305 
4484 


18214 
17936 


2785 


As  is  seen,  the  reduced  volumes  differ  only  in  the 
first  decimal  place.  But  as  the  units  are  doubtful,  the 
tenths  are  not  significant.  As  the  tenths  in  228.5  ^s  °-5> 
the  number  according  to  custom  is  increased  to  229.  It 
is  thus  manifest  that  the  abbreviated  operations  give  as 
good  results  as  the  detailed  one. 


FORMS   OF   RECORD   OF   DATA 

It  always  saves  time  and  energy  to  enter  data  as  soon 
as  obtained  in  some  approved  tabular  form.  Always 
use  a  note  book,  never  a  scrap  of  paper.  Preserve  all 
the  arithmetical  work  so  that,  if  necessary,  it  may  be 
checked  up  with  a  second  determination.  Some  forms 
of  tabular  entries  are  given  at  the  end  of  the  directions 


Forms  of  Record  of  Data  xxxv 

for  the  performance  of  various  experiments.  A  very 
common  operation  in  quantitative  work  is  the  fol- 
lowing : 

A  dish  or  other  vessel  is  weighed,  some  substance 
placed  in  it,  and  a  second  weighing  made.  The  differ- 
ence in  the  weights  gives  the  weight  of  the  substance. 
A  good  form  of  record  for  this  operation  is  this  : 

Wt.  of  dish,  crucible,  or  test  tube  +  substance =  47. 63^"- 

Wt.     '" =  23.42^- 

Wt.  of  substance =  24.2i<?"- 

Suppose  a  substance  is  being  heated  to  constant 
weight  in  an  evaporating  dish.  A  convenient  form  of 
record  is  the  following : 

Wt.  of  dish  +  substance  after  heating  for  20  min =  47.84^- 

Wt.      "        +          "  "  <4         "    10     "     more  =  47.67^- 

Wt.      "         +          "  "  "         "    10     "        "      —  47.63  <£•• 

Wt.      "         +        .."  "  "         "    10     "         "      =  47.63*-- 

Wt.      " =  23.42^- 

Wt.  of  substance =  24.21^- 

Other  similar  forms  may  be  readily  devised  by  the 
student.  It  is  a  good  plan  to  decide  upon  what  form 
of  record  is  to  be  used  before  commencing  a  quantita- 
tive experiment.  The  very  preparation  of  a  form  often 
helps  wonderfully  in  keeping  track  of  the  steps  in  an 
experiment. 


APPENDIX  F 


LABORATORY   EQUIPMENT 

The  subjoined  lists  contain  the  apparatus  and  the  chemicals 
required  for  the  experiments  in  this  book.  Prices  and  quantities 
have  not  been  given,  but  the  author  will  be  pleased  to  give  infor- 
mation to  teachers  using  the  book  as  to  the  quantities  of  apparatus 
and  chemicals  used  by  his  own  classes.  Prices  may  be  obtained 
from  any  of  the  dealers  in  chemical  supplies. 


LIST  A 
INDIVIDUAL  APPARATUS 

This  list  comprises  the  pieces  of  apparatus  constantly  used  by 
a  single  student,  who  should  be  provided  with  each  piece. 

Iron  tongs. 
Platinum  wire. 
Blowpipe. 
Iron  forceps. 
'Triangular  file,  6". 
'Round  file,  8". 
Wire  gauze  or  asbestos  board. 
'Wing-top  burner. 
Mortar  and  pestle,  4". 
Iron  spoon. 
2 Deflagrating  spoon. 
2Glass  rod,  5". 
Two-hole  rubber  stopper  to 

fit  large  test  tubes. 
3   ft.  rubber  tubing,  3/4e". 
3   ft.  glass  tubing,  medium  wall, 
to  fit  rubber  stopper. 


6  Test  tubes, 
6  Test  tubes, 
2   Test  tubes,  9x1". 
Beaker,  100  c.  c. 
Beaker,  250  c.  c. 
Flask,  100  c.  c. 
Flask,  250  c.  c. 
Retort,  250  c.  c. 
Glass  plates,  4x4". 
Thistle  tube. 
Funnel,  2^". 
'Porcelain  crucible,  i  oz. 
'Pipestem  triangle. 
Evaporating  dish,  3". 
2Test-tube  holder. 
2Test-tube  brush. 
Test-tube  rack. 


1  These  pieces  of  apparatus  may  be  used  by  several  students  in  common. 

2  These  pieces  of  apparatus  may  readily  be  made  by  the  student  himself. 

[ xxxvi ] 


Laboratory  Equipment  xxxvii 

LIST  B 
TABLE  APPARATUS 

This  list  includes  the  apparatus  which  should  be  kept  at  the 
laboratory  desk  used  by  the  student  or  on  a  side  table.     It  is  a 
part  of  the  equipment  to  be  used  by  different  classes. 
i    Retort  stand  with  two  rings          'Mohr  pinch-cocks. 

and  a  clamp.  'Iron  and  copper  wire. 

6   Wide-mouthed    bottles    or          'Sand. 

receivers.  'Graduated  cylinders,  100  c.  c. 

i    Pneumatic  trough.  and  500  c.  c. 

i    Bunsen  burner.  'Bar  magnets. 

3   ft.  rubber  hose  for  attaching          'Splinters  of  wood. 

Bunsen  burner.  'Wax  tapers. 

1  "Acid  bottles. "  'Meter  sticks. 

'Assorted  corks.  'Trip  scales  and  weights. 

'Hofmann  screw-cocks.  'Chaslyn  balances. 


i  It  is  not  feasible  to  give  quantities  for  these  articles ;  as  many  as 
possible  should  be  provided,  although  it  is  possible  to  get  along  with  few. 

LIST  C 
DEMONSTRATION  APPARATUS 

This  list  comprises  the  apparatus  which  the  teacher  should 
have  for  demonstrating  experiments.  It  should  be  of  the  best 
quality  and  not  mere  makeshift. 


i    Eudiometer  and  trough. 

i    Electrolysis  of  water  appa- 


ratus. 


i    Safety  tube. 

i    Kipp's  gas   generator  (it  is 


Thermometer. 
Bulb  tube. 
Induction  coil. 
Battery  to  run  coil. 
Large  lamp  chimney. 


well  to  have  two  or  three  'Rubber  stoppers  of  various 

all  charged  and  ready  to  sizes. 

deliver  at  any  time   such  'Ignition  tubes. 

gases  as  hydrogen,  carbon  'Supply    of    glass    tubing  of 

dioxid,  etc.).  various  sizes. 

2    U-tubes,  6"  and  8".  'Supply  of  rubber  tubing  of 
i    Liebig's  condenser.  various  sizes. 

i  Refer  to  note  in  List  B. 


XXXV111 


Elementary  die  mist  ry 


LIST  D 

CHEMICALS 

The  chemicals  should  as  far  as  possible  be  of  "  c.  p."  grade. 


Acid,  acetic. 

citric. 

hydrochloric. 

nitric. 

oxalic. 

pyrogallic. 

sulfuric. 

tartaric. 
Alcohol,  ethyl. 

methyl. 
Alum,  chrome. 

potash. 
Aluminum,  metal. 

sulfate. 
Ammonium,  chlorid. 

hydroxid. 

nitrate. 

oxalate. 

sulfid. 

Antimony,  metal. 
Arsenic,  metal. 
Arsenious  oxid. 
Asbestos. 
Barium,  chlorid. 

nitrate. 
Bismuth,  metal. 

nitrate. 

Bleaching  powder. 
Borax. 

Cadmium  chlorid. 
Calcium,  carbid. 

carbonate  (marble). 

chlorid. 

fluorid. 

oxid  (lime). 

sulfate  (gypsum). 


Carbon  bisulfid. 
Charcoal,  animal. 

wood. 
Coal,  hard. 

soft. 
Cobalt,  chlorid. 

nitrate. 
Cochineal. 
Copper,  metal. 

nitrate. 

sulfate. 
Ether. 
Glycerin. 
Indigo, 
lodin. 
Iron,  metal  (filings  and  wire). 

chlorid. 

sulfate. 

sulfid. 
Lead,  metal. 

nitrate. 

monoxid  (litharge). 

red. 
Litmus, 

paper. 

Magnesium,    metal   (powdered 
and  ribbon). 

sulfate. 
Manganese,  dioxid. 

sulfate. 
Mercury. 
Mercuric  chlorid. 

nitrate. 

oxid. 

Mercurous  nitrate. 
Nickel  chlorid. 


Laboratory  Equipment 


XXXIX 


Phenolphthalein. 
Picture  cord  (iron). 
Potassium,  metal. 

bromid. 

carbonate. 

chlorate. 

chromate. 

dichromate. 

ferricyanid. 

ferrocyanid. 

hydroxid. 

iodid. 

permanganate. 

sulfate. 

sulfocyanid. 
Rosin. 

Silver  nitrate. 
Soda-lime. 


Sodium,  metal. 

bicarbonate. 

carbonate. 

chlorid. 

hydroxid. 

nitrate. 

phosphate. 

silicate. 

sulfate. 

sulfite. 

Stannous  chlorid. 
Starch. 

Strontium  nitrate. 
Sulfur,  flowers  and  roll. 
Tin,  granulated. 
Vaseline. 
Zinc,  granulated  and  sheet. 

sulfate. 


APPENDIX  G 


REFERENCE   BOOKS 


DICTIONARIES 

COMEY,  Arthur  Messinger.     Dictionary  of  Chemical  Solubilities. 

New   York:     The  Macmillan  Co.     $5.00. 
HOPKINS,  Albert  A.     Scientific  American  Cyclopedia  of  Receipts. 

New  York:     Munn  &*  Co.     $5.00. 
WATTS,  Henry.     Dictionary  of  Chemistry.     Revised  by  Morley 

and  Muir.     New  York:    Longmans,  Green  &^>  Co.    4  vols. 

$65.00. 

DESCRIPTIVE  CHEMISTRY 

HOLLEMAN.      Inorganic    Chemistry.      Trans,   by    Cooper.      New 

York:     John    Wiley  &*  Sons.     $2.50. 
JONES,  Harry  C.     Principles  of  Inorganic  Chemistry.     New  York: 

The  Macmillan  Co.     $4.00. 
MENDELEEFF,  Dimitry  Ivanovitch.    Principles  of  Chemistry.    New 

York:    Longmans,  Green  &*  Co.     2  vols.     $10.00. 
NEWTH,  G.  S.     Text-book  of  Inorganic  Chemistry.     New  York: 

Longmans,  Green  &*>  Co.     $1.75. 
OSTWALD,    Wilhelm.     The    Principles    of    Inorganic    Chemistry. 

New   York:     The  Macmillan  Co.     $6.00. 
REMSEN,    Ira.      Chemistry.      (Advanced    Course.)      New    York: 

Henry  Holt  6-  Co.     $2.80. 

ROSCOE,  Sir  Henry  Enfield&  Schorlemmer,  C.     Treatise  on  Chem- 
istry.    (First  two  Volumes.)    New  York:    D.   Appleton  &* 

Co.     $15.00. 


THEORETICAL  AND  PHYSICAL  CHEMISTRY 

DOBBIN,  L.  &  Walker,  J.     Chemical  Theory  for  Beginners.    New 

York:     The  Macmillan  Co.     jo  cents. 
JONES,  Harry  C.     Elements  of  Physical  Chemistry.     New  York: 

The  Macmillan  Co.     $4.00. 

[xl] 


Reference  Books  xli 

VAN    DE VENTER,    Charles.      Physical    Chemistry  for  Beginners. 

Trans,    by    Boltwood.     New    York:     John  Wiley  &»   Sons. 

$1-50. 
WALKER,    James.     Introduction    to    Physical    Chemistry.     New 

York:     The  Macmillan  Co.     $3.00. 

HISTORICAL  CHEMISTRY 

LADENBURG,  Dr.  A.     Lectures  of  the  History  of  the  Development 

of  Chemistry  Since  the  Time  of  Lavoisier.     Trans,  by  Dobbin. 

Chicago:  The  University  of  Chicago  Press.     $7.75. 
MEYER,  Ernest  von.     History  of  Chemistry.     Trans,  by  G.  Mc- 

Gowan.     New  York:  The  Macmillan  Co.     $4.50. 
MUIR,  Matthew  Moncrieff  Pattison.     Heroes  of  Science,  Chemists. 

New  York:  Thomas  Nelson  &*  Sons.     $1.50. 
RAMSAY,  W.     Gases  of  the  Atmosphere.     New  York:    The  Mac- 
millan Co.     $2.00. 
THORPE,  Thomas  Edward.     Essays  in  Historical  Chemistry.  New 

York:  The  Macmillan  Co.     $2.25. 
VENABLE,  Frank  Preston.     Short  History  of  Chemistry.     Boston: 

D.  C.  Heath  &*  Co.     $1.00. 
VENABLE,   Frank  Preston.     Development  of  the   Periodic  Law. 

Easto n,  Pa.:  Chemical  Publishing  Co.     $2.50. 
ALEMBIC  Club  Reprints.     Chicago:     The  University  of  Chicago 

Press.     4.0  cents  each. 
REPRINTS  of  Science   Classics.      Chicago :    The   School  Science 

Press.    5  and  10  cents  each. 

ORGANIC  CHEMISTRY 

BERNTHSEN,  A.     Text-book   of   Organic  Chemistry.      Trans,  by 

McGowan.     New  York:  D.  Van  Nostrand  Co.     $2.50. 
GATTERMANN,  Ludwig.     Practical  Methods  of  Organic  Chemistry. 

Trans,  by  Shober.     New   York:   The  Macmillan  Co.     $1.60. 
LASSAR-COHN.     Laboratory  Manual  of  Organic  Chemistry.  Trans. 

by  Smith.     New  York:  The  Macmillan  Co.     $2.25. 
ORNDORFF,  W.  R.     Laboratory  Manual  in   Organic  Chemistry. 

Boston:  D.  C.  Heath  &*  Co.    jj  cents. 
REMSEN,  Ira.     Organic  Chemistry.     Boston:  D.  C.  Heath  &*  Co. 

$1.20. 
RICHTER,  Victor  von.     Organic   Chemistry.      Trans,   by  Smith. 

Philadelphia:  P.  Blakiston  Son  &>  Co.     2  vols.     $6.00. 


xlii  Elementary  Chemistry 

INDUSTRIAL  AND  ANALYTICAL  CHEMISTRY 

JULIAN,  Frank.  Quantitative  Chemical  Analysis.  St.  Paul:  The 
Ramsey  Publishing  Co.  $6.00. 

THORP,  Frank  Hall.  Outlines  of  Industrial  Chemistry.  New 
York:  The  Macmillan  Co.  $3.50. 

WAGNER,  Rudolph  Johannes.  Manual  of  Chemical  Technology. 
New  York:  £>.  Appleton  &>  Co.  $1.50. 

ALUMINUM  and  Aluminum  Alloys.  Pittsburg,  Pa.:  The  Pitts- 
burg  Reducing  Co.  $1.50. 

MISCELLANEOUS 

DANA,  Edward   Salisbury.     Minerals  and  How  to  Study  Them. 

New  York:     John    Wiley  &*  Sons.     $f.jo. 
GREENE,  H.     Coal  and  Coal  Mines.     Boston:  Houghton,  Mifflin 

<S^>  Co.     75  cents. 
HARDIN,  Willett  L.     Rise  and  Development  of   Liquefaction  of 

Gases.     New  York:   The  Macmillan  Co.     $1.50. 
HOPPING.     The  Practical  Study  of  Common  Minerals.     Chicago; 

The  School  Science  Press.     60  cents. 
JOHNSTON,    James   Finlay  Weir.      Chemistry  of    Common   Life. 

New  York:  D.  Appleton  &>  Co.     $2.00. 
KIMBALL,   Arthur   L.      Physical   Properties  of  Gases.      Boston  : 

Houghton,  Mifflin  &>  Co.     $1.25. 

LASSAR-COHN.     Chemistry  in  Daily  Life.     Trans,  by  Muir.    Phil- 
adelphia: J.  B.  Lippincott  &*  Co.     $1.50. 
SHENSTONE,  William  Ashwell.     Methods  of  Glass-Blowing.     New 

York:  Longmans,  Green  &*  Co.    50  cents. 
THORP,  Frank  Hall.     Inorganic  Chemical  Preparations.     Boston: 

Ginn  &*  Co.     $1.50. 


THE  INDEX 


ACETALDEHYDE,  338 

Alcohol,  335 

Antimoniuretted    hydro- 

Acetates,  340 
Acetic  acid,  339,  340 
glacial,  340 

ethyl,  336 
methyl,  336 
Alcoholic  liquors,  337 

gen,  245 
Antimony,  240,  241 
acids,  248 

Acetylene,  89-91 

Aldehydes,  338 

oxids,  244 

as  an  illuminant,  90 

Alkali,  defined,  148 

Sulfids.    2A.A. 

Acid,  acetic,  339,  340 

early  meaning,  146,  183  Apatite,  236  ~" 

benzoic,  351 

fixed,  183 

Aqua  f  ortis,  1  60 

boric,  261 

metals,  183-198 

Argentite,  297 

butyric,  342 

volatile,  183 

Argon,  63 

carbolic,  351 

Alkalin  earth  metals,  251- 

Arsenic,  239 

citric,  342 

259 

acids  and  salts,  248 

fuming  nitric,  162  • 

reaction,  151 

greens,  248 

gallic,  352 

Alkaloids,  352 

history,  239 

hydriodic,  180 

Allotropy,  30 

occurrence,  239 

hydrobromic,  179 

Alum,  281 

oxid,  243 

hydrochloric,  177 

burnt,  55 

preparation,  240 

hydrocyanic,  85 
hydrofluoric,  178 

tanning,  282 
Aluminum,  278 

properties,  240 
sulfids,  244 

hypophosphorous,  246 

acetate,  340 

trioxid,  243 

lactic,  341 

alloys,  280 

uses,  240 

malic,  342 

bronze,  280 

white,  243 

metaphosphoric,  247 

carbonate,  283 

Arseniuretted  hydrogen, 

nitric,  1  60 

chlorid,  283 

245 

nitrous,  162 

hydroxid,  281 

Arsenopyrite,  239 

oleic,  342 

metallurgy,  278 

Arsin,  245 

orthophosphoric,  247 

occurrence,  278 

Atmosphere,  97-103 

oxalic,  341 

oxid,  282 

Atomic  heat,  220 

palmitic,  342 
phosphorous,  246 

properties,  279 
silicates,  283 

•theory,  138-142 
Atomic  weights,  200-212 

picric,  351 

sulfate,  283 

determination,    214- 

pyrophosphoric,  247 

uses,  280 

222;  by  Avogadro's 

pyrosulfuric,  234 

Amalgams,  186,  274 

hypothesis,  206 

salicylic,  351 

Amethyst,  264 

of  alkali  metals,  198 

silicic,  266 

Ammonia,  64 

Atoms,  138 

stearic,  342 

history,  64 

Avogadro's   hypothesis, 

sulfuric,  229 

liquid,  65 

203-206 

sulfurous,  228 

occurrence,  64 

Azote,  62 

tannic,  352 

preparation,  64 

tartaric,  341 

properties,  65 

BAKING  powders,  195 

Acid  reaction,  151 

soda  process,  194 

Barite,  251 

salts,  21  1 

uses,  68 

Barium,  252 

Acidity  and  basicity,  210 

water,  65 

nitrate,  259 

Acids,  147,  339 

Ammonium,  186 

sulfate,  259 

defined  in  terms  of  ions, 

a  radical,  122 

Base,  defined,  148 

15° 

as  ion,  153 

defined    in    terms  of 

early  meaning,  146 

chlorid,  189 

ions,  150 

nomenclature,   152 

hydroxid,  187,  188 

early  meaning  of,  146 

preparation,  166,  167 

sulfate,  193 

Bases,  insoluble,  167 

Acker  process,  170,  187 

sulfid,  192 

nomenclature,   152 

Adsorption,  65 

Amygdalin,  351 

preparation,  167 

Air,  97 

Amyl  acetate,  343 

soluble,  167 

and  life,  102 

valerate,  343 

Basic  salts,  2  1  1 

composition,  99 

Analysis,  50 

Basicity  and  acidity,  210 

density,  97 

of  organic  compounds, 

Bauxite,  278 

history,  97 

134 

Beer,  80,  337 

liquid,  98 

of  water,  5  1 

Benzene,  90,  349,  350 

mixture,  100 

Anglesite,  288 

Benzine,  96,  350 

solid  matter  in,  101 

Anilin,  351 

Benzoic  acid,  351 

weight,  97 

Anthracite,  73 

aldehyde,  351 

[  xliii  ] 


xliv 


Elementary  Chemistry 


Benzol,  350 

Beryllium,  251 

Bessemer  process  for  steel 

311 
Bismuth,  242 

oxids,  244 

trisulfid,  244 
Bituminous  coal,  73 
Bleaching,  171 

by  sulfur  dioxid,  228 

powder,  255 
Blowpipe,  n  6 

qxyhydrogen,  36 
Boiling  point,  5 
Boneblack,  73,  74 
Borax,  262 
Boric  acid,  261 
Boron,  261 
Boyle's  law,  1 7 
Brandy,  337 
Brass,  272 
Bread,  347,  348 
Bricks,  284 
Brimstone,  223 
Bromin,  173,  174 

hydrate,  174 
Bronze,  272 
Bunsen  burner,  1 1 1 ,  112 

flame,  in 
Butyric  acid,  342 

CADMIUM,  273 

sulfid,  273 
Calamine,  271 
Calcite,  251 
Calcium,  251,  252 

carbonate,  255 

chlorid,  254 

fluorid,  255 

hydroxid,  254    . 

light,  36 

oxid, 253     - 

phosphate,  258 

sulfate,  257 

sulfid, 258 
Calomel,  275 
Calory,  58 
Carat,  304 
Carbohydrates,  344 
Carbolic  acid,  351 
Carbon,  70-75 

bisulfid,  226 

compounds,  77-96,  332 
335 

gas,  75 

occurrence,  70 

properties,  70 

valency,  332,  333 
Carbon  dioxid,  7  7 

composition,  81,  82 

formation,  78 

occurrence,  77 

preparation,  78 

properties,  78,  79 

uses,  80 
Carbon  monoxid,  80 

composition,  82 


Coke,  75 
Collodion,  348 
Combustible,  1 06,  107 
Combustion,     28,     104, 

106,  107 

in  Bunsen  flame,  in 
in  candle  flame,  109 
in  coal  stove,  81 
of  organic  compounds, 

133 
187         spontaneous,  107 

Compounds  and  elements, 


CARBON  MONOXID  —  Cont.   Cocaine,  352 

preparation,  80 

properties,  80 

uses,  81 
Carbonado,  70 
Carbonates,  77 
Carbonic  acid  gas,  7  7 
Carbonic  anhydrid,  77 
Carborundum,  266 
Carnallite,  184,  251 
Cassiterite,  286 
Castner's  process,  170 
Catalysis,  27 
Celestite,  251 
Celluloid,  349 
Cellulose,  348 
Cerussite,  288 
Chalcedony,  264 
Chalcocite,  294 
Chalcopyrite,  294 
Chalk,  77 
Champagne,  80 
Charcoal,  73,  74 
Charles'  law,  1 5 
Chemical  change,  4,  7 

action,  6 

equations,  52,  127,  133 

equilibrium,  66,  190 

properties,  5 

Chemistry,  importance  of, 
13 

organic  and  inorganic, 
86 

study  of,  3 


and  mixtures,  10,  n 
Condenser,  39 
Conservation  of  energy, 
12,  59 

of  matter,  1 2 
Contact  method  for  sul- 

furic  acid,  233 
Copper,  294 

alloys,  295 

compounds,  296 

history,  294 

metallurgy,  294 

nitrate,  296 

occurrence,  294 

oxids,  296 

plating,  297 

properties,  295 

purification,  294 

sulfate,  296 

sulfid,  297 

uses,  295 


thermo,  58  uses,  295 

Chile  saltpeter,  62,  184,  196  Copperas,  317 
Chlora),  338  Coral,  77 

Corrosive  sublimate,  275 
Cream  of  tartar,  342 


Chloral,  338 

hydrate,  338 
Chlorate  of  potash,  197 
Chlorid  of  lime,  255 
Chlorin,  168 

history,  168 

hydrate,  172 

liquid,  172 

manufacture,  169 

occurrence,  168 

oxids,  1 80 

preparation,  168 

properties,  171 

uses,  172 
Chloroform,  338 
Chlorophyll,  79 
Choke  damp,  87 
Chromates,  322,  323 
Chrome  alum,  322 
•ironstone,  321 

steel, 


Crocoisite,  32 1 
Cryolite,  194,  278 
Cupel,  298 
Cupellation,  298 
Cuprite,  294 
Cyanogen,  85 


D ALTON'S  law,  23 
Davy  safety  lamp,  106 
Deacon's  process  for  chlo- 

rin,  169 

Decomposition,  60 
Deflagration,  29 
Deliquescence,  56 
Density,  5,  17 
Dewar  bulb,  98,  99 
Dextrin,  347 

o.^,  .,.1  Dextrose,  346 

Chromic  compounds,  322      Diamonds,  70 
/-M .-i.    .  Diatomaceous  earth,  264 


Chromite,  321  

Chromium,  321-323  Diffusion,  35 

Chromous  compounds,  321  Dissociation,  60 

Cinnabar,  273  electrolytic,  theory  of, 

Citric  acid,  342  148 

Clay,  278  laws  of,  190 

Coal,  72,  73  of    calcium    carbonate, 

Coal  tar,  349  256 

Cobalt,  319  Distillation,  39 


The  Index 


xlv 


Dolomite,  251 

Dulong  and  Petit's  law,  220 

Dumas'  method  of  density, 


214 
Dutch    method 

lead,  292 
Dynamite,  348 


for    white 


EARTHENWARE,  284 
Efflorescence,  56 


gold,  3o( 
Electro  -  chemical    equiva-  Formaldehyde,  3  3  8 

lents,  202  Formalin,  338 

Electrolytes,    mass    action  formula,  122,  123 

in,  190 
Electrolytic    dissociation,     ,,    meaning,  124 

I4g  Formula  weights,  127 


FLAME  —  Continued  Graham's  law,  35 

oxidizing,  116  Graphite,  71 

oxyhydrogen,  36,  108     Gun  cotton,  348 
reducing,  116  Gunpowder,  29,  196 

speed    of    propagation,  Gypsum,  223,  257 

in 

structure,  108  HALID  salts,*  1 68,  188 

temperature,  no  Hall's    process    for    alu- 

Fluorin,  173  minum,  278 

Fool's  gold,  306,  316  Halogens,  168 

compounds,  245 
oxygen  compounds 
of,  if 


determination,  125,  126  Harveyized  steel,  311 
Heat,  58,  104 
Hematite,  306 


process  for  chlorin,  170  Freezing  point  of  solutions,  Hydracids,  152,  176 


Electrons,  138 
Elements,  7  Furnace,  blast,  114,  307 

classification,  330  electnc,  115 

immutability,  12  muffle,  113 

table,  9  reverberatory,  114 

unknown,  prediction  of,        shaft,  114 

33° 

Emulsin,  352  GALENITE,  223,  288 

Endothermic  reaction,  58      Gallic  acid,  352 
Energy,  2,  12  Garnierite,  318 

conservation  of,  12,  59  Gas,  14 


Epsom  salts,  254 
Equations,  52,  127 

balancing,  128 

molecular,  143 

usefulness  of,  133 
Equivalent   proportions, 

law  of,  203 
Equivalent  weights,  200 

of  compounds,  202 

and      atomic      weights 

compared,  208 
Equivalents,  200-203 

and  valence,  208,  209 

electro-chemical,  202 

system  of,  201 
Esters,  342,  343 
Ethane,  334,  335 
Ether,  ethyl,  339 
Ethers,  339 
Ethyl  acetate,  342 

alcohol,  336 

but y rate,  343 

ether,  339 

Ethylene,  89,  91,  334 
Eudiometer,  43 
Exothermic  reaction,  58 
Explosions,  112 

FACTORS,  6 
Fats,  343 
Feldspar,  278 
Ferro-manganese,  309 
Filters,  41 
Filtration,  40,  41 
Fire  damp,  87 
Flame,,  105,  106 

Bunsen,  1 1 1 

candle,  109 

luminosity,  108 


carbon, 75 

illuminating,  91 

marsh,  87 

natural,  95 

volume,  reduction,   18, 

19 

water,  93 
Gases,  modes  of  measuring, 

21 

properties  of,  14-25 
Gasoline,  96 
Gay-Lussac  tower,  232 
German  silver,  272 
Glass,  267 

Bohemian,  269 

bottle,  268 

coloring,  269 

flint,  268 

manufacture  of,  267 

painting  on,  269 

properties  of,  267 

window,  268 
Glauber's  salt,  192 
Glover's  tower,  231 
Glucose,  346,  347 
Glucosides,  351 


Hydrazin,  68 
Hydrazoic  acid,  68 
Hydraulic  cements,  269 
Hydriodic  acid,  180 
Hydrobromic  acid,  179 
Hydrocarbons,  87,  95 
Hydrochloric    acid,    177, 

178 

Hydrocyanic  acid,  85,  86 
Hydrofluoric  acid,  178 
Hydrogen,  33  t- 

antimonid,  245 

arsenid,  245 

chemical    properties, 
35 

compounds,  244  . 

diffusion,  35 

dioxid,  56 

disulfid,  226 

history,  33 

ions,  153 

liquid,  35 

nascent  state,  35 

occurrence,  33 

physical   properties. 

phosphid,  245 

preparation,  33 

sulfid,  224,  225 

uses,  36 
Hydrolysis,  167 
Hydroxids,  33,  152 

of  alkali  metals,  186 
Hydroxyl,  a  radical,  122 

as  ion .153 

Hypophosphorous     acid, 
246 


Glycerin,  337,  343,  344,  348  "Hyposulfite  of  soda,"  235 

Gold,  302 

ICE,  manufactured,  66 
Identification 


alloys,  303 
compounds,  304 
fool's,  306,  316 
history,  302 
metallurgy,  302 
occurrence,  302 
plating,  304 
properties,  303 
separation  from  silver, 

303 
uses,  303 


of    sub- 
stances, 5 
Ignition  point,  105 
Illuminating  gas,  91 

history,  91 
manufacture  by    old 

process,  91 
natural,  95 
properties,  95 
water-gas  process,  93 


xlvi 


Elementary  Chemistry 


Indicators,  152                        Lead,  288 

Mercurous  chlorid,  275 

Infusorial  earth,  264                    acetate,  292,  340 

nitrate,  275 

lodin,  175,  176                                alloys,  290 

Mercury,  273,  274 

oxids,  1  80                                  black,  71 

Metaboric  acid,  262 

lodoform,  338                                 carbonates,  292 

Metals  and  non-metals,  8 

lonization  theory,  149                  chlorids,  291 

Metaphosphoric  acid,  247 

Ions,  153                                           chromate,  323 

Methane,  87,  88,  91 

reactions  of,  154                      compounds,  290 

Methyl,  334,  335 

Iron,  306                                         dioxid,  291 

alcohol,  336 

acetate,  340                              history,  288 

benzene,  350 

cast,  309                                    metallurgy,  289 

salicylate,  351 

chlorids,  317                             nitrate,  291 

Methylene,  334,  335 

compounds,  315                       occurrence,  288 

Mica,  278 

galvanized,  272                        oxids,  290 

Milk  of  lime,  254 

hydroxids,  316                         properties,  289 

of  sulfur,  223 

metallurgy,  306                       red,  291 

sugar,  346 

occurrence,  306                       sulfate,  291 

Mineral  waters,  39 

oxids,  316                                  sulfid,  291 

Mixtures  and  compounds, 

pig,  308                                      uses,  290 

IO 

properties,  313                         white,  292 
pyrites,  306,  316              Lead  pencils,  71 

Molasses,  345 
Molecular  weights,  200- 

sulfates,  317                      Liebig's  condenser,  40 

212 

sulfids,  316                        Lignite,  73 

determination  ,     214- 

varieties,  308                    Ligroin,  96 

222 

wrought,  309                     Lime,  253 

by  Avogadro's  hy- 

Isomerism, 335                              milk  of,  254 

pothesis,  204 

Isomers,  335                                   slaked,  254 

Molecules,  138 

water,  254 

Molybdenum,  323 

TACT>T?T?      f.                           Limestone,  256 
JASPER,  264                           Liquid,  14 

Mordants,  282 
Morphine,  352 

•^                                                          air   98 

Mortar,  269 

ammonia,  65 

Moth  balls,  351 

KAOLIN,  278,  284                       chlorin,  172 

Kelp,  193                                     _   hydrogen,  35 
Kerosene,  96                          Liquidation,  242,  286 
Kipp's  gas  generator,  34       Litharge,  290 

NAPHTHALENE,  351 
Nascent  state,  35  • 
Nitrobenzene,  351 

Lithium,  184 
LAC  SULFURIS,  223             Lodestone,  306,  316 
Lactic  acid,  341                       Lunar  caustlc»  297,  3oo 

Nitroglycerin,  348 
Neutral  reaction,  151 
Nickel,  318,  319 

Lactose,  346 

Niter,  196 

Lampblack,  75 

Nitric  acid,  160-162 

Laudanum,  352                      MAGNALIUM,  280 

fuming,  162 

Law,  Boyle's,  17                     Magnesium,  252 

Nitric  oxid,  158,  159 

Charles',  15                                chlorid,  254 

Nitrids,  63 

Dalton's,  23                              hydroxid,  253 
Dulong  and  Petit's,  220         oxid,  253 

Nitrogen,  62 
dioxid,  159 

Graham's,  35                           sulfate,  254 

history,  62- 

of  conservation  of  en-  Magnetite,  306 

occurrence.,  62"^ 

ergy,  12,  59                    Malachite,  294 

oxids     and     oxacids, 

of  conservation  of  mat-  Malic  acid,  342 

155-163 

ter,  12,  50                      Manganates,  325 

pentoxid,  159 

of  constant  heat  sum-  Manganese,  323,  324 

peroxid,  159 

mation,  83                             oxids,  324 

preparation,  /62 

of  definite  proportions  Manganous  salts,  324 

properties,  63- 

by   mass,  or   weight,  Marble,  251 

tetroxid,  159 

46,  49                              Marsh  gas,  87 

trioxid,  159 

of  definite  proportions  Massicot,  290 

weight,  207 

by  volume,  45,  49         Matches,  239 

Nitrous  acid,  162 

of  dissociation,  190         Matter,  2 

Nitrous  oxid,  156,  157 

of  equivalent  propor-            conditions  of,  14 

Nordhausen  oil  of  vitriol, 

tions,  203                              conservation  of,  1  2 

234 

of  multiple  proportions,        constitution  of  ,  138 
57                                    Melting  point,  5 

OIL  of  bitter  almonds  ,351 

of  nature,  i                        Mercuric  chlorid,  275 

of  vitriol,  234 

of    volumetric    propor-        nitrate,  275 

Oils,  343 

tions,  45                                 oxid,  274 

Olefiant  gas,  89 

Le  Blanc's  process,  193               sulfid,  275 

Oleic  acid,  342 

The  Index 


xlvii 


Opal,  264 
Opium,  352 

Plaster  of  Paris,  257 
Plastering,  269 

Salicylic  acid,  351 
Salt,  defined.  148 

Orpiment,  239 
Orthophosphoric   acid,  247 
Osmotic  pressure,  217 
Oxalic  acid,  341 

Platinum,  304,  305 
Plumbago,  71 
Polymerism,  335 
Polymerization,  90 

defined  in  terms    of 
ions,  150 
early  meaning  of,  146 
Glauber's,  192 

Oxidation,  28 

Polysilicic  acids,  267 

making,  188 

Oxidized  silver,  299 

Porcelain,  284 

rock,  189 

Oxidizing  agent,  29 

Portland  cement,  269 

Saltpeter,  160,  184,  196 

flame,  116 
Oxids,  29 

of  alkali  metals,  186 
of  alkalin  earth  metals, 
252 
of  chlorin,  180 
of  iodin,  180 
Oxygen,  26 

Potash,  195 

by  alcohol,  187 
by  lime,  187 
Potassium,  184^ 
bromid,  191 
carbonate,  195 
chlorate,  197 
chromate,  323 

Salts,  nomenclature,  152 
preparation,  164-166 
Sandstone,  264,  265 
Saponification,  343 
Sapphire,  282 
Scheele's  green,  248 
Schweinfurt's  green,  248 
Sea  water,  39 

compounds,  242-244 

cyanate,  198 

Seidlitz  powder,  342 

history,  26 
nomenclature,  29 
occurrence,  26 
preparation,  26,  28 

cyanid,  197 
ferricyanid,  317 
ferrocyanid,  317 
hydroxid,  186,  188 

Selenite,  251 
Serpentine,  251 
Siderite,  306 
Silica,  264. 

properties,  28 
reduction,  29 

iodid,  191 
nitrate,  196 

amorphous,  26? 
Silicates,  267 

uses,  30 
Oxyhydrogen  blowpipe,  36 

occurrence,  184 
permanganate,  325 

Silicic  acids,  266 
Silicon,  263 

Ozone,  30-32 

preparation,  184 

dioxid    264. 

Ozonizer,  31,32 

properties,  185 

hydrid,  265 

PALMITIC  acid,  342 
Paper,  349 
Paraffin,  96 

sulfate,  193 
Precipitate,  41 
Pressure,  14 

measurement  of,  15 

occurrence,  263 
preparation,  263 
properties,  264 
tetrachlorid,  265 

Paregoric,  352 
Paris  green,  248,  340 
Parkes'  process  for  silver, 
298 
Pearl  ash,  196 

osmotic,  217 
Prussic  acid,  86 
Puddling,  309 
Purple  of  Cassius,  304 
Pyrargyrite,  297 

tetrafluorid,  266 
Silver,  297 
alloys,  299 
bromid,  300, 
chlorid,  300 

Periodic  law,  328 
Periodic  system,  326-331 
Periodic  table  of  elements, 

Pyrites,  223 
Pyrophosphoric  acid,  247 
Pyrosulfuric  acid,  234 

compounds,  299 
German,  272 
history,  297 

329 

metallurgy.  298 

Permanganates,  325 
Petroleum,  95,  96 

QUARTZ,  264 
Quicklime,  253 

nitrate,  300 
occurrence,  297 

Phenol,  350 

Quinine,  352 

oxid,  300 

Phenyl,  350 
Phlogiston,  116 

RADICALS,  122 

'  oxidized,  299 
plating,  299 

Phosphates  and  their  uses, 

Reactions,  6 

properties,  298 

247 

acid,  151 

sterling,  299 

Phosphin,  245 

alkalin,  151 

uses,  299 

Phosphoretted  hydrogen, 
245. 

neutral,  151 
reversible,  66 

Smalt,  319 
Smithsonite,  271 

Phosphorite,  236 

substitution,  171 

Smoke,  no 

Phosphorus,  236 

Reagents,  6 

consumer,  no 

acid,  246 

Realgar,  239 

Soap,  344 

chlorids,  245 

Reduced  volumes,  19 

Soapstone,  251 

history,  236 

Reducing  agent,  29 

Soda,  187 

occurrence,  236 

flame,  116 

ash,  194 

oxids,  242 

Reduction,  29 

washing,  195 

preparation,  237 

Rhigolene,  96 

water,  80 

properties,  237 

Rock  candy,  345 

Sodium,  184 

red,  238 

Ruby,  282 

acetate,  340 

uses,  238 

copper,  294 

bicarbonate,  195 

Photography,  301 
Physical  changes,  4 

SAL  AMMONIAC,  64,  189 

carbonate,  193 
chlorid,  188,  189 

constants,  5 

Sal-prunelle,  196 

hydroxid,  186-188 

properties,  5 

Sal  soda,  195 

nitrate,  196 

Picric  acid,  351 

Saleratus,  195 

occurrence,  184 

xlviii 


Elementary  Chemistry 


SODIUM  —  Continued 

SULFUR  —  Continued 

Vapor  tension,  2  2 

preparation,  184 

occurrence,  223 

of  water,  53 

properties,  185 
salicylate,  351 

preparation,  223 
properties,  224 

Verdigris,  295,  340 
Victor  Meyer's  method  for 

sulfate,  192,  193 

roll,  223 

vapor  density,  216 

thiosulfate,  234 

trioxid,  228 

Vinegar,  340,  341 

Solid,  14 

uses,  224 

Vitriol,  blue,  296 

matter  in  air,  101 

water,  39 

green,  317 

Solubility,  54 

Sulfuretted  hydrogen,  224, 

Voltameter,  51 

product,  191 

225 

Volumes,  132 

Solute,  54 

Sulfuric  acid,  229-234 

measurement  of  ,  15 

Solution,  54,  65 

fuming,  234 

a  conductor  of  electric- 

Sulfurous acid,  228 

ity,  150 

Superphosphate     of    lime,  WATER,  38 

boiling  point,  219 
freezing  point,  218 
Solvay's    ammonia-soda 

237,  248 
Supersaturation,  55 
Supporter    of    combustion, 

analysis,  51 
distillation,  39 
filtration,  40 

process,  194 

106 

formation,  42 

Solvent,  54 

Symbols,  120 

gas,  93 

Specific  gravity,  1  7 

Synthesis,  50 

gravimetric  measure- 

heat, 220 

ments,  47 

Spiegeleisen,  309 
Sphalerite,  271 
Stalactite,  257 
Stalagmite,  257 
Stannic  chlorid,  288 
oxid,  287^ 

TANNICACID,  352 
Tanning,  352 

alum,  282 
Tannins,  352 
Tartar  emetic,  342 
Tartaric  acid,  341 

hard,  257 
mineral,  39 
of  crystallization,  55 
physical     properties, 

purification  of,  by  fil- 

sulfid, 288 
Stannous  chlorid,  288 

Temperature,  kindling,  105 
of  flames,  no 

tration,  41 
rain,  38 

oxid,  287 
siilfid,  288 

Temperatures,  absolute,  16 
high,  modes  of  attain- 

river, 39 
sea,  39 

Starch,  347 

ing,  113 

spring,  38 

Stearic  acid,  342 

measurement  of,  15 

synthesis,  50 

Steel,  310 
Bessemer  'process,  3  1  1 

Tempering  of  steel,  3  1  o 
Tests,  6 

vapor,  22 
volumetric    composi- 

cementation   process, 

Tetraboric  acid,  262 

tion,  43-45 

311 
Harveyized,  311 

Thermolysis,  279 
Thermometers,  15 

Weights,  atomic,  200-222 
atomic    and    equiva- 

open-hearth   process, 

Thiesulfuric  acid,  234 

lent  compared,  208 

313 

Tin,  286 

combining,  118,  123 

tempered,  310 

alloys,  287 

elemental,  118,  123 

Stibin,  245 

chlorids,  288 

equivalent,  200 

Stibnite,  223,  241 

foil,  286 

formula,  127 

Stoneware,  284 

history    286 

molecular,  200-222 

Strontianite,  251 
Strontium,  251 

metallurgy,  286 
occurrence   286 

table,  119 
Weldon  process,  170 

nitrate,  259 

oxids.  287 

Welsbach  light,  1  1  2 

Substances,  2 

identification  of,  5 

properties,  286 
stone,  286 

Wine,  337 
Witherite,  251 

Sugar,  345 

sulfids,  288 

Worm,  condenser,  39 

beets,  345 

uses,  287 

brown,  345 

Tinned    -on,  287 

cane,  345 

Toluene,  350 

ZINC,  271 

fruit,  346 
granulated,  346 
grape,  346,  347 

Touch-paper,  196 
Transpiration,  35 
Tungsten,  323 

blende,  223,  271,  273 
chlorid,  272 
metallurgy,  271 

milk,  346 

Tuyeres,  308 

occurrence,  271 

of  lead,  292 

oxid,  272 

Sulfids,  226 
Sulfur,  223 

URANIUM,  323 

properties,  271 
sulfate,  273 

allotropic  forms,  224 

sulfid,  273 

compounds,  228 
dioxid,  227,  228 

VALENCE,  I43-I4S,  332 
and    equivalents,    208, 

-      uses,  272 
vapor  density,  272 

flowers  of,  223 

209 

white,  272 

milk  of,  223 

Vapor  density,  17,  214 

Zincite,  271 

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